Start with structural stuff first: window seals, any
leaks, floor patch, frame,
axle, etc. People tend to focus on the cosmetics first and lose steam before critical structural repairs are made.
You want it leak tight and road worthy. Everything else is secondary. Myself, I do not use systems until I have tested them (electrical, plumbing, and propane), particularly on a 20 year old trailer.
Having a covered work area is VERY desirable. Even one of those temporary Harbor Freight carports can work (depends on your local rules).
Inspect the
windows carefully. If you see signs of silicone caulk on the outside, I would assume that window leaked (and may well be still leaking) and would be high on my priority list.
Fiberglass itself does not leak (unless it has been damaged). Its where holes were cut (rivets,
windows, vents, etc). Those can leak. Once the water gets into the trailer, it heads to the floor. Then you get floor rot. Its the cycle of
leaks. Plumbing leaks inside are already in the trailer, and head to the floor as well. Floor rot is the result of a leak, not the source.
Google is your friend. Every single repair you might face has been done in the past by others. Check out the manufacturers section too. Some repairs are Scamp specific, others aren't.