It is easy to do using prefab panels. Lay up the prefab on a sheet of glass or other smooth surface (abitibi board works well), cut it to size and add vertical edges. Glue the ipe to them and you have a totally waterproof locker lid that will be plenty strong and will never rot. Two layers of 1708 with layers of mat on each side will make a nice stiff panel. You could also glue this prefab to the inside of your cockpit to minimize finishing if you start the layup with a rolled on coat of gelcoat. You could get away with two layers of mat for the cockpit sides. If I was building your cockpit I would build the entire thing from prefab and skip the plywood. I would make a cored panel with 1/2" core cell for the sole - skip the gelcoat on the sole.