I own vintage conversion with 43 years old fiberglass cap.
It shows aging, but holds, while I keep the coach protected from UV.
Gellcoat can be resprayed and this is a project I am planning for my canoe, but would hesitate for RV as the surface might not come perfectly smooth.
I think it would take extreme deterioration for fiberglass to leak, but with gellcoat chalked out - automotive painting is valid option.
Advantage of paint v/s gellcoat is that for paint you can prep/prime the surface, while gellcoat is more like 1-time application.