I recently installed a fiberglass turtle to prevent water from entering the cabin via the main hatch. It is made from 1/8 inch boat making foam and covered with fiberglass. The foam can easily be cut to shape and glued together with super glue. It was then saturated with epoxy. Internal ribbing was installed for structural strength--it can be stood on without flexing--then fiberglassed with more epoxy. The turtle was finished with primer, Brightside one part enamel all around and added non-skid on the top. Photos can be seen in my member profile.