[Ed]

John B-

I have done my fair share of recoring hatches (both marine ply and divinycell).

If you don't have too many things that get screwed into the hatch and rely on it (the hatch for support) than I would go with the divinycell. It is waterproof, lighter and pretty easy to work with. You can lay it down in either a wet layer of 1.5 ounce mat or you can trowel in Divinlite (Divinycell's own putty) and lay the Divinycell in that.

Marine ply isnt a bad way to go either. Like Fellowship said, it adds some weight which isnt always a bad thing. Just make sure that all holes for inspection hatches, mounting screws, etc. are coated with epoxy/cabosil mix and you should be ok.

Ed