I bought mine at HD also. The package of foam I used says Frost King Self-Stick High Density 3/8" rubber foam weatherstrip. It's 3/8" wide x 5/16" thick. It seams like it compresses real easily, but only when compressed between my fingers. When the hatch is pressing over the area of the entire weatherstrip there is more resistance.

My friend Cid and I took the "Triple Play" out on Lake washington with some pretty good waves coming over the deck and the back when we were launching. The hatches were completely buried by the waves a couple of times until we could get away from the edge of the shore. When I got home that evening I opened the hatches to dry them out, but they were completely dry. Not one drop. If I remember right, the foam does soak up a little water though.

: Dale,
: On the subject of hatch covers, where do you get closed cell gasket mat'l?
: I bought some at Home Depot that said closed cell and it doesn't let much
: water into the hatch but the gasket itself gets soaking wet. I'm thinking
: of cutting some out of seat/bulkhead foam.
: Ray