Very nice trailer!
I'm going through similar planning options. Since road and off road hazards are difficult to predict the critical damage areas are more difficult to protect. Everything is a compromise, I could do the sides in plate steal but the weight creates all kinds of issues. Regardless of how thick plywood might be a loaded trailer sliding sideways into a rock ledge will suffer damage, from stress to the ply to punching a hole or cracking the panel. So, nothing is bullet proof, part of the fun taking risks. And, money is an object in most builds.
So I've been looking at what the pros do, the manufactures. Sheet aluminum seems to be king, but there are different grades some softer than others, I've not researched that yet. It also requires a master welder for best results, I don't care for the idea of screwing, bolting or riveting aluminum, but I suppose those are options, aluminum boats have rivets and I've seen 50 year old boats on the water. Adhesives are another option for light applications.
Hey, I woke up at 3 AM, but I will get to a conclusion. I'll get to it.
The Jumping Jack trailer is very similar to what I have, my frame is heavier, but it has expanded steel on framed sides, typical tilt lawn tractor/bike hauler with a drive up tail gate that locks in 3 positions. Don't recall the gauge of the expanded sheets, but it's stout. My thought is lighter ply box with a good epoxy paint inside the frame and expanded steel outside the frame painted the same color. The 1 1/2 inch gap gives some space to protect the box. It's also a great space for mud and dirt to build up, so frequent cleaning would be necessary.
The expanded steel has taken some hits that would dent sheet metals or cracked wood and bounced back in form. The lighter expanded steel seems to stretch and become wavy on some trailers, drive up ramps, mine has not, but covered sides don't take that kind of use and at that point it can be cut off and replaced in a damaged area or section.
It's certainly a different look, not a slick camper but a more utility looking. Might paint it with bed liner stuff.
Wonder what gauge would make it bear proof? Brown bears, maybe not grizzles.
As to the floor, I have steel plate. I'll have plywood as a box floor with treated wood skids about 3/4 inch thick on the bottom holding the floor off the steel. I'm thinking about using cork flooring inside, softer walk, insulates, easy to clean, sealed it's water proof.
Last thought, steel trailers with aluminum parts, what about electrolysis issues between metals and electrical grounds?
