[warthog5]

With the anchor hatch in mind, I'd go ahead and buy the hatch.
Then build a parimeter frame on the underside while it's upside down.
Then have a piece of overlap core for and aft of that to span the cut.

Set the hatch so the hinge's are to the side. [Port side]
What this does is get the hatch out of the way when your deploying or retriving line.

I saw this setup first on a Teira and it work's well, as apposed to having the hinges foward or aft.