|Re: the locker lid - You don't need to buy a pre-made lid - the triangle you cut out of the deck becomes the lid. If you cut slowly and carefully with a high-quality jigsaw (Makita or Bosch), the most material you will remove (the "kerf") will be around 3/32", which is a gap you'll need for the hatch to open smoothly anyway. True, you'll have to drill a hole to start the saw, but it you do it where one of the hinges will be placed, you won't see it.
When I saw this job in progress, I had my doubts, but by using a matching gelcoat and working carefully, the fellow did a job that you had to look at twice to tell it wasn't a factory anchor locker.
C&C 27 Mk IV