Originally Posted by TomKeffer
You're on the right track.
It's easier to get a smooth surface if you pile the epoxy on a little proud, then sand down so it's slightly (very slightly) concave.
I need 10 mills for the gel coat, right? That seems like a lot. If the area being filled is concave, then the gel coat will be very thin at the edges of the hole. Will that cause it to fail?