If you can get fully to the inside and remove all of the rotten wood that was laminated to the fiberglass sheeting, I think I would leave the outside alone and glue panels to the inside. clamping the pieces together would be a problem, a large C clamp thru the window would anchor some of it. If you cut up the outside fiberglass sheeting, unless you replace the entire side or very large section, it will end up looking like a tacked together mess, JMHO.
a board could be nailed to the floor in the cabinet to push out against the bottom and somebody here parked next to a building and pushed against the outside wall to glue things back together.
good luck, and keep us posted.
bumpy
