In my limited experience, I've not seen much water in there.  However, I have removed one set of the rather ratty trim and see that the interior shell is not well mounted or sealed.

I seem to recall that there was a lot of shredded paper or something most likely used to support the compartment while the sealer set up.

Your idea might provide a decided improvement.  If lockable, it would provide more secure storage.

Steve in San Jose
Dawson 26, "Banana Split"
Hull 270

You can get the following hatches with locks (special order).

http://www.marinesurplusinc.com/servlet/Detail?no=911

The size is adequate in terms of height.  But the width is short buy about .75".  The plan is to obtain 3 hatches and make a bezel out of delrin to make up the difference:

http://www.mcmaster.com
part: 8573K35

-josh