Finding replacement bolts and lugnuts for trailer wheels is not terribly easy. Most auto supply shops carry... automobile parts. But with a patient sales associate that let me come in the back, I was able to rustle through the drawers and find ten bolts and nuts that matched the dimensions needed to replace the rusted out ones. The nuts are a bit long, but I think it adds some character.
The floor is a sandwich of 3/8" plywood, 2x4's laid flat, and luaun plywood. Everything has been glued, screwed, and urethaned at least twice. Maybe three times on the bottom. Still, I think another layer of protection might be a good idea.