[BigLew]

I know that West Marine carries a gasket material that should work. It is a hollow "HOSE" made of a foam material similar to neoprene- heck it probably is neoprene. It has a adhesive strip running down the outside inorder to attach it to the hatch. This will probably need some fortification for durability purposes, but should work resonably well. The tricky part will be forming a water tight connection where the two ends of the gasket butt together.

Good luck.