: I am using the Schade designed hatch and screw locking device. Unfortunately
: my hatches have curved a bit and so they do not seal all the way around on
: the gasket material I used. Any suggestions on what gasket material might
: be thick enough and flexible enough to seal all the way around the hatch
: and where I can find it.

I'm not familiar with the Schade design however I had a similar problem with the curve changing & was able to successfully deal with it by covering both lips with saran wrap & tape then liberally applying thickend black epoxy (use graphite) - I "squished" the hatch down over the hatch lip till it was as far as it would go, then let it set up - with a quick run over on the sander I had a perfect fit & being black you can't see it from a foot away.