I am not your expert, so this is just some old experience I had when I used to paint cars. I normally just primed and painted the fiberglass. But once I had some T-Tops that had been damaged and repaired. When I primed, crows feet shot up all over them. No matter how many times I sanded and sealed, they came back. I finally gel coated, primed and painted and it worked great. What I took away from it was that undamaged panels did fine without gel coat. Repaired panels might benefit from the gel coat. It will be interesting to see what more experienced painters have to say. :thumbsup:

BTW, not sure how it is done now, but the stuff I used was one thick, self-curing coat. I think I had to change the spray gun nozzle to be able to spray it.

 

My car has been painted by a friend of mine and me twice in the last 20 years. My car was panted by somebody else before I bought it and must have been stripped mostly by sanding and in alot of places the gelcoat is missing. We have used the sandable sprayable filler/primer with great success. Gel coat is the more correct way if you are a purest but I never seen it used so cannot give you the pitfalls good luck

 

If the fiberglass is hairy (ie the panel has been sanded enough to expose the fibers) then you need to put some form of gel coat to seal the fibers back into the panel. If you have no fibers then go ahead and prime. If you do prime and after sanding notice fibers poking up, sand that area down, apply gel coat and reprime.