: Pygmy kayaks use flush-mount deck cut-outs for hatch covers. Yes, they use a
: spacer (4 mm) between the deck and the hatch lip. Their hatch kit
: instructions would probably be helpful to you.

: Hint: After gluing the foam gasket, do not cover and compress the foam until
: the glue solvent has completely dried. The foam can be permanently
: compressed from the fumes.
Pygmy's hatches turn out good. They use a firm rubber gasket that is a 1/4 inch thick. It is 1/16 of an inch thicker than the spacer.