I laminated the day hatch hole cut-out to the 6" plastic hatch cover, and I glued the plastic rim to the inside of the deck so all you see is wood (except for the small cut-out for the flush "T" handle). The quarter turn "T" handle works very fast for quick access (it is opposed by a lip on the other side), and the cover mates with the rim nicely on a relatively soft 1/4" dia glued in "O" ring. I added a tether to keep track of the lid. It has proven to be perfectly watertight. I'm glad I don't have to worry about buggering up the threads of a spinner type hatch.

The only improvement I would like is a hinge. Making a watertight hinged hatch shouldn't prove difficult, just design the height of the lid so it squashes the foam or "O" ring a bit more than you want then remove that excess squash factor by shimming under the hinge. The shim can be replaced by shims of different heights to give you an adjustable amount of pressure on that end of the hatch. It would probably be a good idea to match the pressure applied by the cam latch, or whatever the fastening mechanism is, at the other side of the hatch. It would also be a good idea to reinforce the hatch lid with perpindicular mounted wood slats, so the hatch shape will not deform over time, of course multiple dogs and a compliance hinge would yield the highest degree of watertight integrity.