re: companionway hatch for a boat

One answer is to use plywood for the panels and epoxy them in. Floating panels are not a seaworthy construction.
I have done lots of raised panel doors for sailboats where the doors are not large using half lapped corner joints and glued in panels, all epoxy. I have never had a failure. Red Cedar however, while high in rot resistance, is not anywhere near as dimensionally stable as teak and not really hard enough to take the beating that doors get.
Another possibility if the doors are larger is to glue/seal the doors in with a polysulfide (like Thiokol) or polyurethane (like Sikaflex) which have some give and stretch a little.

How big are the doors and what kind of boat is it?