OK. I've repaired a few
seals for hatches, but not made one from scratch. It goes like this: Wrap the
hatch cover in thin kitchen wrap or thin tape. With the old seal in place, spread silicone on the mating surface, with a thick layer wherever there is a tear or foam missing. Press the cover down onto the sticky seal, and leave it until it sets. The kitchen wrap may adhere to the wet silicone, so careful trimming of the renewed seal is in order.