There is a much easier and quicker way to do this using doorskin or another thin plywood (okume?). I happen to be doing it the other way in order to maintain consistent wood color but here is the method for your perusal:

Firstly glue a 2-3" strip of vertical grain ply all around the opening. Just let it overhang and don't worry about it. After glue up, plane it flush with the deck and then mark up the recess profile w/ a pencil and then plane to that line.

Secondly overlap the base past the downturn and glue. Keep the grain at 90deg to the boat if you have big curvature of the recess. Then glue on a 1" high strip all around for the upturn.

Next glue on the lip. Then plane the i/s lip and the i/s base at the same time. Then the outside base.

Add glass and its done.

May work too!

-mike