As others have said, buy a TC that is built like a boat hull (i.e. fiberglass). That's what holds up.
Fiberglass truck campers are basically a boat without the mast. The problem is, a nice new fiberglass truck camper will set you back over $40k. There just aren't a lot of folks willing to pay that amount of money, so most are built much more cheaply.
btw, I disagree that most cargo trailers are built better than RVs. I've seen enough of them rattle apart on washboarded roads to not be over enthusiastic about their build quality