Not much to it really, I've good results gelcoat over West System Epoxy. Just make sure the epoxy is absolutely cured (like a week), cleaned thoroughly (water/soap to remove amine blush), and sanded with nothing higher than 220 grit to give a decent mechanical bond. Our N20 boards and rudders were repaired with epoxy (the rudders quite extensively) and when I ran out of time, I gave to a local boat guy to finish up. I expected him to use Imron (since I know he prefers it), but he knew I preferred gel coat and finished them in gel coat. They've got approximately 700 miles on them and they still look great - even in the areas where the rudders rub the castings going up and down.