Sounds like a project! This forum is all about all-MOLDED fiberglass
(i.e., egg-type trailers like Scamp
and Casita), so we're pretty specialized. You'll likely get more help with the kind of laminated construction you're describing in a general RV forum.
The issues you experienced are exactly what brought many of us to molded fiberglass
does make a larger 25' molded fiberglass model. It's set up for four-season living. Pricey new, but with patience I bet you could find a used one for less than the cost of completely rebuilding the one you've got. Just sayin'...
Best wishes, whatever you decide.