David Pascoe says that many hatch covers into below deck areas do not
seal because the plastic flexes too much, he says this is especially
true of the larger ones.
So, make em from G10. Yes, def more expensive than the molded plastic
ones but strong as hell. You'd have to use 3/8" thick G10 with ribs
of 3/8 " across the back attached with screws and 5200. The frames
could have good O-ring seals cut by CNC. They would be strictly
"screw down" not intended for normal opening but for occasional
inspection.
Not yet sure the frames could be made of multiple pieces to avoid
waste (of the cut out). Maybe G10 can be glued with epoxy, I am not
sure.
It might be cheaper to make the frames from epoxy/glass and then
flycut it.
Does anybody make wood that has had epoxy impregnated via pressure?