What will u tow it with? That van?
Aluminum is light. It will not rust as easy. In CO you dont have salted roads so that is all I know that are the biggie benefits.
I have a steel 1 inch square tubing (for the box) framing. No rust, they paint it, and I keep it dry, as there are no leaks.
A little rust on the frame is not a big deal, it will be decades for a frame to rust out unless u live in a salty place.
Steel is easy for me to weld on and infinetily reparable.
Steel is stronger, and can flex over and over without breaking. Aluminum will eventually crack if flexed a lot, guessing you will take it off road, so there could be flexing...
Cargo trailers are built to be abused, they are built strong.
Everything you build in it might be a different story.
The weakness will be the axles (hubs) and leaf springs if going down washboard a lot. Look into Timbren stuff if u plan to go crazy with off roading.
I put windows in mine that fit between the wall studs, 22 inch wide windows in my case. This is not necessary but does maintain strength.
Build it light. You do not need 1/2 plywood inside. Plan to attach cabinets directly through the paneling to the steel studs, not to a heavy plywood wall. Make notes with a sharpie on the wood where the frame studs are, this can be hidden at top or bottom, and make note at top and bottom as many trailers are not built so precise that you can be sure the stud is not crooked. Build light! my mottos is "no 2x4's were used"
Do insulate the roof with at least 2 inches. 1 inch on the walls, if that is the stud thickness, is fine.
You said base camp, so yes, cargo trailer will be super durable and hold up many many times better than a camper would, and this is one reason why ppl build off of cargo trailers.
Go solar. 200-300 watts at least. MPPT controller. Solar is king. Plan that from the start. Plan your electrical wiring run so you run wires before the walls are up. Put in "future" wiring so you have the wire there if you want changes or additions.
