This material from CLC seals very well and is more dense than the standard "Frost King" open cell foam you might get at the local Home Depot. I found that the adhesive creeps rapidly when subjected to shear and could only get a single season out of it.

http://www.clcboats.com/shop/products/boat-building-supplies-epoxy-fiberglass-plywood/boat-fasteners-hardware/foam-hatch-tape.html

I recently replaced the above with:

http://www.amazon.com/gp/product/B000HE7YQM/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1
I will let you know next August if I like it any better.

You might also consider using internal bungie cord, you can apply more downward force on the hatches than with anything external.