: I would then cut a hole to about an inch of the inside
: the coaming, and sew the skin to the inside of the coaming and
: paint to waterproof.

Interesting that you decided to paint it before attaching the coaming - I hope that works for you. Your plan sounds fine - but you might want to give it more than an inch. I usually fold the fabric over once or twice, and sew through that.
You should still be able to heat shrink the fabric with the paint on (carefully!), if you can't get it to conform perfectly to your coaming.

Good luck - I'm looking forward to seeing both ya'lls boats!

Dave