I wanted to keep the boat a light as possible so decided to use 1/4" okoume as much as possible. This requires adding stiffeners under the deck to minimize flex but needed to be light. I ended up using blue foam to create a form which I covered with glass.

This shows the rear deck with stiffeners. The bulkhead also adds support in the middle.

This shows a closeup of the stiffener. I used one layer of cloth, 10 strands of heavy glass strand, followed by another layer of cloth. The glass strand provides a strong unidirectional layer that is very light