I’ve been looking at building one same material and methods just not as wide and using more common components.
Before investing that much into what is essentially an overbuilt utility trailer, I would take some serious time to think about your intended use case and what level of durability you'll actually require.
I'd argue that for the vast majority of us, a $900 utility trailer from the local Walmart would be more than sufficient.
I have a 5x10 "folding frame" trailer that I bought for about $900 some four years ago. I bolted down some 3/4" plywood flooring, used 2x10 pressure treated lumber for sidewalls and tailgate, added three 8ft long e-tracks and called it a day. The trailer is galvanized steel, c-channel. Almost certainly (can't remember) made in China, simple and basic. I've used this trailer to haul 4500lbs of flooring, tons of appliances and furniture, 3000lbs of gravel, and of course, all our camping gear several hours on forest service roads. The trailer is no worse for wear despite all the abuse.
(Admittedly, I did blow a tire when I had it under-inflated and overloaded.)
Short of ramming my trailer into trees/rocks, I simply cannot imagine a scenario in which I damage it during any camping trip.
And here it is hauling my new barrel sauna home this past Tuesday: