The fiberglass repair will only be as good as the adhesion you get. I't important to make sure the metal is clean and rough where the fiberglass is attached. The adhesion also depends on what type of resin you choose, the standard prompted poly-ester doesn't stick as well as say epoxy, but should be fine so long as you get a good clean rough surface for it to grab onto. Something like 60 or 80 grit or even angle grinder wheel finish is how rough you want it.