Making an Off Road Trailer. (Redux)

First off I made a huge mistake and accentually deleted my instructables account. Long story short remember that Autodesk and instructables are the same. The old archive of the article is |here| luckily the internet is forever, well at least the text is.

The wife and I wanted to have an off road capable trailer. Since we have the capabilities we decided it would be a cheaper and more robust option for us to build it our self. Many people decide to take a cargo trailer and modify it for off road use but we decided to build one from the ground up.

I am going to have most of this instructable from the point of us working on the project, its a custom job for our needs your needs may differ, what I am showing is one of many ways to go about making this project.

I did make a build log of the trailer as it was under construction you can find it |here|, note it is not a how-to but how I did most of the work.

Lots and lots of supplies to make life easy but you really only need a basic tools.

Do you even need a trailer?

This was the first question we asked our self and the answer was no, but we would like a trailer as it would allow us to pack all of our camping gear and spare parts in the trailer allowing us to keep the vehicle near empty this would be safer for us as there are less things in the cab that can come free and hit you and it would make setting up camp much faster as it is already set for us.

Do you buy or build?

We looked around at several companies from pop up campers to specialty utility trailers. Often the cost got us to around half the cost of the FJ and there were compromises as it wasn't our plan but someone else's. We also couldn't justify a dedicated camper trailer as we have a 2 car garage and we couldn't see us using half of it for something that can't hold cargo if we need to use it like a truck bed. This all pushed us to build our own trailer.

What do you want it to do?

Sounds simple, drag behind and camp in. Well, it gets more complex, we never used a trailer to camp in and you can see in the pictures we originally came up with a hatch style system to access everything in the bed. We decided to make the trailer in 2 phases.

Phase 1 was to make the trailer as a 4'x6' truck bed.

Phase 2 to put a lid on it.

We decided this as we really don't know what we would need if our cargo happens to be 30" square and the hatches we made were 28" so we decided to make the trailer and see how we use it before moving to phase 2.

How big of a trailer?

You can find examples of trailers that are less than 4'x4' with small tires up to 30' dual axle monsters. We wanted a trailer that would hold about a truckload of gear, use the same wheels and tires as the tow rig and have a rack on the top to hold a tent. This got us to a trailer about 12' long with a 4'x6' box and sat about the same height as the truck. We also didn't want to have the trailer stick up above the vehicle so we picked out a tent we wanted and made sure the top was about the same height as the vehicle.

You need to have a plan.

I have a degree in engineering and access to Autodesk Inventor so I went to town on the plan. I have seen people build a trailer off not much more than pencil sketch on some scrap paper and do just fine. I was able to design it to know the approx weight and weight loading of the trailer. Once you figure out what your going to build your trailer out of there are many many websites that tell you how much metal shapes weight per linear foot, so you can do this by hand. Its not impossible.

Plan for safety.

Trailers are simple tools provided you do 2 things.

1. Have proper frame strength.

If the frame is too weak you will have the tongue bend and fail. The center spar of my frame is 2 1/2" square by 1/4" thick, the rest of the trailer is 2" square by 1/8" thk. You also have to make sure the trailer doesn't weight too much.

2. Have proper tongue loading.

A vehicle can only take so much load on the ball of the hitch and if a trailer doesn't have enough weight forward of the axle it looses stability. Trailers can be designed correctly and still packed wrong so this rule is something you need to keep in your head the whole time.

I used a PDF from Dexter Axle on how to place an axle you can find it |here|

License the trailer.

Take a look at your state/local government's laws for trailers. In TX I was able to licenses this trailer as a equipment trailer as it was under the weight and not technically designed as an RV. For this I just went up to the county office and filled out a piece of paperwork and got some plates that day, the trailer wasn't even done yet, no inspection.

Still need to keep it legal.

Once again take a look at your local laws, in TX for the weight I didn't need trailer brakes but I still needed rear lights, license plate light and reflectors.

The hitch

There is more than just a ball hitch out there. The ball is the cheapest and should get you most places just fine but we chose to go with an AT max coupler, it is designed to have no binding that a ball does. The coupler is also designed to go into a 2" receiver on both sides, this is one of the reasons we chose to have the center spar be 2 1/2" x 1/4" square tube.

Build a solid base.

Everything is built off the frame of the trailer this means the simplest looking part is really the most critical. It needs to be square and strong. If this is wrong everything else will be wrong. I took my time on this part and even cut it apart and restarted on it because it wasn't good enough.

Don't trust your concrete floor to be level, unless your building on a specialized table or planed floor your going to have an un level floor. I thought on for this project I would be ok but it was over 1/4" twisted. I had to cut my tack welds and re check with a level. It was worth it.

Critical point!

This doesn't look to be a critical point, its just a piece of metal that sticks out of a box. Well it takes the weight load of the trailer and connects it to your vehicle. If all your connections are in line they will be in a high risk of cracking and if it is made too short you can run it to issues of turning.

Strong strong strong.

This part is the last section of the trailer that needs to be strong as you can be. The area from the cargo box to the ball can be the weakest area. Even when not being towed the tongue takes the weight as the ball jack is on the front of the trailer. The tongue never takes a break.

If you noticed on the last step I made the frame stick out past the farthest up cross members. I did this so I can can trim them down and weld along it so the weld is diagonal to the load it will see. It is a simple thing to do but something you need to plan for.

A bit more beef since we plan on throwing around the trailer.

We decided to take a 2"x1/4" flat bar and plate the ends. We opted to wrap the corner to act as a bit more protection in case we run the trailer into rocks and trees. This also helps beef up that welded location as is spreads out the connection point.

Got to make a bent part with a welder "minimal" tools.

I don't have a proper way to bend metal, I don't have a torch or press but I do have an angle grinder, table vise, welder and a hammer. I scored the plate where I want to bend, clamped it to the vice and hit it with the hammer until I got the shape I wanted. Lined it up with the frame and trimmed the frame to fit the plate just right and welded it in. I also then went back and welded the score line, this puts metal back that I cut out and the heat helps relieve some stresses from cold forming the metal.

This step is relatively easy. If you follow the PDF I linked at the earlier, once again its |here|. They do a good job on telling you where to place your axle, if you are doing this in a very manual fashion you might want to hold off until later so you can balance the trailer to find out the best location of the axle.

The devil is in the details. I wanted to use the same wheels and tires as the tow rig. In this case its a 2013 FJ Cruiser. I didn't think about the studs being metric or SAE. I figured I could just get some SAE nuts that fit the wheels. That wasn't true, the nuts for the wheels only come in metric so I had to buy a metric spacer to act as an adapter to fit my wheels.

This isn't 100% true, you can still do work on the bottom of the trailer but its easiest to do right now. I decided to gusset the cross member that lines up with the spring hangers.

Time to start building the functional trailer parts!

Instead of building panels and trying to get them to match perfectly I opted to build a skeleton then later come back and skin it. Since the skeleton isn't taking a huge amount of load I made it out of 1 1/4" square by 1/8" thk. I tacked most of the frame together then came back and seal welded it.

The top of the trailer has a ladder type rack to hold the roof top tent we will be installing.

Use the space you have don't let it go to waste.

Many people install a tongue box, we opted to put space for, four (4) gas cans, this helped move weight forward and it is out of the cargo area so it is not likely to get damaged by anything moving around in the cargo bed.

I used, I believe, 10 guage (.120" thk) steel for the base and 14 or so for the walls. I had the parts cut and bent by a metal supplier before they arrived to me. I made sure to make them a bit long so I would weld the rounded edge of the square to the plate then grind them down flush. I also fully seal welded the bottom plate and it took forever, and it was done below the trailer, like I said earlier, its possible just not easy. The sides were only welded on the tops and sides. This allows any moisture that gets trapped to fall out.

Welding this much sheet metal took a while and required a lot of tacks to keep the metal from wanting to curl flex. Many people opt to screw sheets on and its a sound method. We opted to weld so there is no chance of screws working loose.

Fenders, spare tire and light pods were installed.

Fenders

Fenders I had subbed out but and cut the exact same then I came back and timed them to fit where they were needed. They also got 1 1/4" square framing along the leading and trailing edge to give them strength to take a hit. The fenders are also 12+ inches deep and flat to act as a table.

Spare tire

A spare tire was added to front of the trailer, this keeps the spare out of the cargo, protects the gas tanks and helps keep that weight forward.

Lights!

We purchased lights that were both brake, turn signal and running lights. Kept the wiring down and fewer holes to drill. The "pod" they are in is designed to once again take a hit and deflect it, that is why the leading edge has a taper to them. When I welded them on to the trailer I welded the top, sides and only the first few inches of the bottom so if water does get in it can fall out.

Wiring

I had to get wire from the front of the trailer to the back. We decided to keep it exposed but inside the bed of the trailer. We used some 1" angle and drilled matching holes on it to loop wire ties to it. This kept it exposed so if for some reason we needed to we can get to it but protected since its inside the trailer and high.

Rear drop legs

If the trailer is not on attached to a vehicle there is a real risk of the trailer tipping backwards if unloaded. Something you do not want if your in a tent on top of it. We installed 2 drop legs behind the fenders. These 2 legs with the front jack make the trailer into a stable tripod when camping.

Rounded edges

At this time we went around the trailer and cut off any sharp edges and round them.

Plan your door.

This can be as complex or easy as you want. Some people even opt to have no rear door if its an exposed bed like ours. We wanted the door to slope to give us some more room with out killing departure angles. The latch is a bought out item and there is one on either side behind the light pods protecting them. The hinge is a 36" stainless steel piano hinge, supper beefy and simple at the same time.

Getting the most out of our door.

This gives us a few cool things we can do with the door:

- A small area to put chairs and commonly accessed items.

- Folded down the door acts as a step or seat.

- If placed half way down we now have a full 4'x8' working bed.

Paint

If you haven't noticed the trailer already had rust on it before I even stated building it. Lots of people rattle can their trailers I choose to powder coat the whole trailer. Very rugged but not cheap.

The inside of the trailer got a roll on bed liner along with some logistics track to hold all my stuff down.

Fabric bits

After it came back from the powdercoat I installed the tent and awing. The awning has a clip that was welded before hand onto the trailer.

This is a new step. We ended up outgrowing the trailer. We knew we would as soon as we had the kid and realized he is going to grow grow and grow. Upcoming I'll post my Camper Build with this 250 flatbed.

This was the last photo of the trailer in our ownership. We were at the parking lot the morning of selling the trailer here.