I'd rather use gelcoat than topcoat. One can put multiple layers without the wax potentially weakening the bond.
Using plastic film on the last layer will make it go off, and if using a smooth plastic sheet, the finish is like on new boat. One can also use hair spray instead of plastic film, easy to wash of later.
Let the gelcoat dry a little before spraying the hairspray, otherwise it might impact on the finish.
fun on a boat is inversely proportional to size...sort of anyway