When I did my Type VII (Amati) I used plastruct 90 degree angle plastic (angle iron) to cover the insides of the openings. It provides sufficient depth, and the curve of the hull with the L-channel inside actually provides an angled appearance internally, similar to the curvature of the pressure hull...
Now the limber holes should be see through, you should be able to see straight through to the other side. I used plywood to create the structural bulkheads above the pressure hull for the deck plating.
Jeff