Contacted Gerneral Paint this is what they said
Paul,
Epoxy as a general rule is applicable over previously painted alkyd substrates. Tremclad falls into that category. With that said you must read the technical data on the specific epoxy you are using. The other option is to do a test to assure adhesion. As for the Fiberglass, General Paint does not deal in Fiberglass and so don't have sufficient info to give you the advice. It would be best to talk to someone that sells Fiberglass and ask about application over alkyd paint.
Tony Blatchford
Sales Support Centre Supervisor
General Paint Corp
604-253-3131
Tremclad is a product of theirs