Cockpit companionway/hatch design-bluewater

Gidday guys,
I have built (nearly) a new deck for my boat. ( And mostly a new hull)
A little at loss as to the provisions for a companionway.
The old was a heavy wooden one on brass runners & it leaked a little.
Probably would be disasterous in an inversion.
Are there proprietry ones available?
We have blanked off the area in solid glass for the companionway and stopped the balsa core short.So we can meachanically fasten to the cutout.
Any ideas greatfully accepted.

 

maybe try to drawing first for your area with computer.. sometime dan making idea better.