"Explorer box" frame design

[DrewsBrews]

I'm looking to build a 6ft long, 2ft tall, 41" wide "explorer box" style trailer to mount one of the rooftop tents to. I picked up the Harbor freight 40.5"x48" kit instead of one of the 48"x96" versions since the narrower axle wasn't a big deal to me and I figured starting light and adding weight as needed is easier than starting heavy and trying to shed as much weight as possible. Now I'm to the point of ditching all but the axle and suspension and building my own simple frame that would be better tailored to the task (HF frame might then become a base for a lawn cart build). I've picked up 8ft of 2x2x1/8" square tube and 16ft of 2x2x1/8" angle and have been playing with design ideas. My current idea would be to build both the box and frame separately and once the box is waterproofed marry it to the frame for final fit and finish. 2x3 lumber would be the floor frame (if even necessary?) and the box itself would be 1/2" ACX or Marine. The box would need to be strong enough to have a 140-210lb tent on top and two+ people. I had planned to add a divider (same 1/2" ply) in the box about 18" in from the front that would add a little extra strength. I have 4 stabilizer jacks so it would be supported at all 4 corners when our weight would be on top. This would only be used on-road and I'm shooting for under 500lb unloaded, but with tent installed. The heaviest items for their size that may go in the box would potentially be a battery or water container.

Here is my latest design idea with the wood frame placed over it.


Stripping the wood away shows the basic steel frame.


The axle would be between the green cross braces and attaching the springs to the side plates.

Not having experience I'm trying to err on the strong side, but I don't know how much of it is really necessary. From looking around it seems the steel cross braces could be omitted and the spring plates attached to the box only... And the wood floor frame might not be necessary if using wood fillets on the inside of the 1/2" ply box? I'm not averse to using thicker ply for the floor if I'm saving the weight and complication elsewhere.

[DrewsBrews]

Here was my initial idea of a long tongue design and using the HF frame with additional wood frame pieces at the front and back. At least it gives a better picture of what I'm attempting to build. Just a simple box really. The more I thought of how I'd attach to the smaller HF frame the less I liked the idea of using it. Also the tongue basket seemed unnecessary to have on all the time if I might not use it often, so I might just use it on the receiver at the back if needed and shorten up the tongue to keep it hugged up to the TV. I'd push the axle back another 6" (incorporated into the above pics) to maintain safe tongue weight with that extra weight hanging off the back and would help a little with backing up since I would lose tongue length. Even if TW ends up near 25% (without basket on the back) it shouldn't be a big deal with the low overall weight. One thing that is not shown is a divider inside the box 18" from the front and a hatch on the front to access that area.

[Dale M.]

Think the 2x2 by 1/8 is a little light for length of tongue even for light weight trailer .. 3x3x1/8 would be better or at at least use a "V" style for tongue if you insist on 2x2 material....

And use of 2x3 lumber is probably over kill if you want to keep things light....

Dale

[DrewsBrews]

Yeah I have pretty much wiped the long tongue idea from my mind; opting to keep it under 36". An alternate idea was to use the angle iron I have on-hand for an A frame tongue but the tongue strength chart lists 36" 2x2x1/8 angle A frame is only good for 660lb trailer weight. However the chart rates a 36" 2x2x1/8 single tube tongue is good for up to 1240lb of trailer so I'll be waay under that.

I've nearly got myself convinced using no frame might work.. Just use beefy wood fillets inside the box, 3/4" ply floor and front side for strength, keeping in mind the divider that will be inside the box also bolstered by fillets to act as a second frame member for tongue attachment. The tongue tube would still go pretty much to the back of the box also with 2" angle welded to the side in spots for additional strength and act as mounting tabs.