This is my first try at flush hatches. I understand that there is a spacer ring and a lip ring below it that the gasket will rest on. I've seen some people use two 1/8th inch spacers followed by the lip ring that has the smaller inner diameter for the gasket to rest on. I have plenty of 1/4" ply and was thinking of one ring of 1/4" for the spacer and one for the lip ring.
Can anyone guide me on what type of gasket material to use and what size it should be? How do you ensure waterproof attachment to the lip ring? Is the gasket material needing to be somehow resistant for the marine environment? I'm going to use bungee loops to hold the hatch down from the inside and am wondering what thickness the gasket material should be so the hatches wind up flush once the downward pressure from the bungee is applied?
Thanks in advance.