I suggest Life Calk
I recently installed the fabric hatch cover, and would advise using a calk such as Life Calk or 5200. The drilling is easy if you follow the manufacturer's instructions on marking the spots where the snaps will attach. Don't worry about the minor cracks in the gelcoat that may appear next to the holes. Steve is right about making sure the hatch is fully closed before you install the cover. I found that rain water pools on top of the cover, and will turn into a "frog pond" if it is not tented up. I used two six inch lengths of water pipe insulation, stood on end beneath the cover, to keep the cover tented up. This worked fine and did not scratch the plexiglass hatch.Don BarberS.V. Third Degree