Prepping a large fiberglass anything for paint is a very large undertaking. Once you start you will basically be committed and part way through you will likely question what you are saving....
For reference, you could read what people go through prepping homebuilt composite aircraft once they have the structure complete. Here is 1 reference Long EZ N28EZ Home Page
Now I will say that with aircraft the builder is trying to accomplish several things simultaneously (right geometry for the flight surfaces, proper balance on the controls, stay within planned weight
and a good appearance). With a camper some of those limitations do not apply but on the other hand the surface area is larger so more work to do.
One of the recent techniques used to avoid pinholes is to wipe the entire surface with epoxy (after is it scrupulously cleaned of all finishes and roughed up for bonding) to seal all pinholes and cover all fibers. Then let that dry until tacky and apply a fairly thick layer of microlight filler. Let that dry until hard, then start sanding with a special long sanding board (the ones they use on aircraft might be 3-4ft long).
Read up on finishing composites. It is a LOT of work. 98% is in the prep. Putting paint on after is easy. Otherwise it will be spray, sand, fill, spray, sand, fill etc etc. A new glossy surface will show every tiniest defect in the finish without mercy.