I'm not making a claim that I know anything about building TC's but I've done my share of boat building and boat mods that have included gel coat applications to storage lockers, boats, cabinets and my utility trailer. If you totally enclose your TC in 3/32" plywood and apply sprayed on gel coating, wouldn't that solve leak issues as it does in a boat? In order to keep a fiberglass or wood boat from condensation buildup we apply a felt cloth like covering over the interior. Although aluminum boats are popular, their condensation issues are somewhat hard to eliminate. Just my $.02 worth.
Also, take a look at Escape trailers built in Canada.
Escape trailers I toured their factory and was impressed with their design and strength. I've always wondered how that could be used in TC's. Bigfoots are somewhat similar in that method of construction.
