Originally Posted by minke
Are you and the manufacturer sure that it is gelcoat? The reason that I ask is that (on boats and maybe trailers) there is a female mold that has the gelcoat applied to it. Then the fiberglass and resin over that, and finally paint on the inside surface.
The norm for cosmetically finishing the reverse side of a fiberglass molding is to apply 'flowcoat' (sometimes called 'topcoat'), which is regular gelcoat resin with about 2% wax in styrene added to it - the wax comes to the surface of the resin and provides the airtight barrier the enables the gelcoat resin to fully cure.
Paint is for more aesthetically-demanding applications, as flowcoat will never give a perfectly smooth glossy finish - though one coat of flow coat is about as thick as ten coats of paint, so it's a lot tougher.
Nowadays I would be surprised if someone like Scamp, who must get through a lot of resin, would bother making flowcoat by adding wax to gelcoat resin - I would expect them to buy it ready-mixed.