2, 1/2" Nida-Core bulkheads, one behind the engine and one in front of the lazarette, both capped with 4" solid fiberglass for bonding the deck panels with your favorite adhesive.
2 longitudinal fiberglass stringers or 1/2" Nida-core bulkheads (also capped and better) from the steering bulkhead to the stern.
1.25" Nida-core deck panels will make the spans needed. A properly pitched deck and a scupper trough at the stern (optional) would preclude the need for a camber.
Materials: 1/2" and 1.25" Nida-core (polypropylene honeycomb core, with film barrier, non-scored); one could also contact Plascore, Zeeland, Michigan for a price quote for the same material.
Lamination both sides (bulkheads and decks): 1708 with 3/4oz mat finish; both taped in with two layers of 1708/DBM (4" and 3") with a 3/4oz mat finish (6").
Strong, durable, light weight, no rot, and proven in both hand laminate and vacuum bag construction for bulkheads, decks, and super structure.