I had the same problem with the SS
Surfside if you look in the last picture you can see I fiberglassed a 3/4" x 2" piece of fir onto the cieling, I used a 1x2" piece to hold it up just slightly "up" to induce a slight curve in the roof.
The skylight actually strengthens the roof as it has a nice aluminum fram and I cut out a large part of the sagged roof.
It is a huge improvement. I am going to replace all the louvered
windows as they are in poor condition. I plan to use tinted plexiglass for privacy as the skylight gives lots of
light inside.
The Daylighter skylight is the same one that they are putting in the new FRP
Bigfoot trailers.
I found a set of mold for a FRP trailer near Vancouver and a boatbuilder friend of mine and myself are thinking of producing kits for do it yourselfers ?