I've done some painting here and there on our boat but I'm no expert
. In bilge areas where water may have a tendency to sit, I used Interlux Barrier Coat...maybe overkill but I didn't feel it was. Other bilge areas I have used the less expensive Interlux Bilgekote. I have also used latex paint that is recommended for bathrooms/kitchens in closets and bulkheads on some of my previous boats. All of them I simply followed the manufactures directions. Cant speak to long term results though.
I recently thought of using the two part epoxy paint made for coating garage floors you can purchased from Home Depot/Lowe's. I would guess it would be satisfactory for a boat interior environment? I cant recall what the cost savings might be or if it would be applicable for FRP though?
I can understand that after you do all the prep, you want to be sure it adheres well and last a looong time. Like most paint projects, most of the work is the prep.
I will try to find some pictures to post