I've been meaning to jump in on the primer aspect of this thread since I've been in the industrial paint industry for the past 15 years. The primer's main function is to adhere to the substrate, in our case a GRP hull. And whether you have a polyester or epoxy lay-up, an epoxy primer will do the best job. It is extremely tough, chemical resistant, and will adhere far beyond our operational requirements. It is also readily available and affordable when compared to automotive lacquer primers.
Once applied, an epoxy primer will accept any type of topcoat, hobby or otherwise. The primer must be sanded first prior to application to ensure the topcoat will bond properly. Two other things cause topcoats to fail over certain primers: if the solvents contained in the topcoat are stronger than what the primer is formulated for, then it will soften the primer and cause it to wrinkle or lift; if the primer is not cured properly and a topcoat is applied, the top film becomes a barrier to the evaporation of the solvent out of the primer coat and prevents it from curing -- then everything comes off in sheets.
I've applied a base coat of epoxy primer to each of my boats. In hull finishing, it accepts putty, and even conventional primers, easily. In service, I've never scratched down to the fiberglass, the primer always holds. And my finish paints, both Floquil hobby paint, and hardware store aerosol enamels, have never failed in service.
For future nuke projects I plan to prime with black and red oxide epoxy primers on the upper and lower hulls respectively to get me that much further down the road. And the occasional scratch that does reveal the primer will be virtually invisible as a result (gray would perform this function well for U-boats).
Edited By PaulC on 1122296566