Welcome, Dan!
Remodeling a broken-down trailer can end up costing more than buying one in camp-ready condition, not to mention the hours you’ll spend. Of course the upside is you can make it exactly what you want.
Comes down to whether you see the remodeling process as an end in itself, something you will enjoy doing, or a means to another end, i.e., camping and travel.
Either way, molded
fiberglass makes a great place to start. There are some great remodeling threads on this forum.