[65Bowrider]

We did a similiar thing as Will for filling in cockpit holes. On the 'finished' side, placed seran wrap, taped into position, clamped wood on finished side for extra security, then filled in hole from underside. All the mess was on the underside and the 'finished' side was smooth...resulting in very little sanding.
If doing lots of little holes, maybe put the duck tape on the 'finished' side and again, fill in from the underside. I was going to try shipping tape...that's clear so you could see & make sure your holes were completely filled & no air pockets. I don't like sanding & avoid whenever possible.