For all but the kayak hatch covers, I use plain old silicone sealer. The important thing is to be sure that when you first install the hatch, you do two things: 1) Make sure that while the glue or sealer is drying, that the cover is screwed firmly into the ring and 2) that you only lightly tighten the screws at first so as not to put the ring in a bind - that would make the cover hard to get on and off later. You can firm them up after the sealer has set up.
