RE: Fiberglass?
Epoxy will bond to almost anything so you will be fine,but if it were me and to save painting id use a small amount of poly resin with some colour additive or gelcoat mixed into a paste with talc if the damage is deep? if not just use gelcoat as Hemi says.gelcoat is cheap and you dont need a lot just get a 500 ml tin and some catalist mix with some talc (usually very cheap from the gelcoat suppliers )to a paste if needed .
Mart