Cut away all of the bad fiberglass
house. Then using sheet fiberglass (from a hardware
store) backed with wood stringers and cut to form an internal mold
with separating wax. Then you can build up a new cabin
side and top. Don't worry about the port lights because you can cut new one in after you are finished fiberglassing.
Or you can cut off the old cabin
top and add carlings to the decks and build an all wood cabin. This two routes you can take and there may be a few more if you think about it. Just remember to use the KISS system. (K