> I'm building a Guillemot and I came up with a flush hatch seal which is
> quite easy to build in comparison to creating a fiberglass lip. (30
> minutes construction time) After cutting out the hatch, I created 3 rings
> of 1/4" ply, to create a recessed lip. the first two layers are
> 1" wide bands which have an I.D. the same as the cut-out so the hole
> is now 3/4" thick including the deck material. A 3rd ring which is 1
> 5/8 wide is the bottom layer. This ring stack is actually cut in two down
> the centerline so it can make the curve of the deck and epoxyed to the
> underside of the opening using 5 minute epoxy. I used spring clamps to
> hold it and in 15 minutes I was done. Now seal the wood with epoxy or
> whatever and install an automotive window seal which slides on the 5/8 lip
> and totally covers all trace of the 1/4 wood. I had some 94 Mercury
> Villager rear gate window seal laying around which worked perfect for the
> above lamination thickness. (the above instructions would have to be
> varied for another seal design, check the Mercury dealer to see what I
> mean) The bottom sealing area of the hatch door should be made smooth so
> the rubber can seal. The finished product is a factory looking watertight
> seal. Use silicone to seal the ends of the seal.

I did something similar_ I used cedar strips as spacers ,then used 3 mm marine ply as the lip ,covered with 1 layer of 6 oz glass.I used 3/8 closed cell foam for the gasket.Closure is with Pygmy's cam buckles on 1" nylon strap.100% dry