The hatch covers are pretty simple to put together. here's the illustrated version:
This is the bottom of the aft hatch cover with 3" fiberglass cloth
waiting for epoxy. The fiberglass adds extra strength but mostly
helps to hold the curve the hatches will have.
Here you can see where the hatch ribs go. The contact side of the
rib is slightly curved (to match the deck) and will bend the hatch
cover when everything is clamped to dry.
This is the forward hatch cover and here you can see more clearly
the curvature the ribs impart on the plywood. The clamps hold the
bend and the ribs in place as the epoxy cures. I should be able to
remove the clamps tomorrow and the curve will remain.