I used the saran wrap and caulk trick to seal my flush hatches. Worked great for me! I used an "exterior" grade clear silicone caulk. Make sure to use clear as you want a little of the caulk to ooze into the gap between the deck and hatch but it doesn't look good if it is white.

I keep hearing about people using "marine" grade caulking. Can anyone tell me the difference between exterior and marine grades. I assume the marine holds up better over time.

Jack