I'm replacing the floor in my old tri-hull boat. After useing the grinder to cut all the rusted screw heads off the plywood I finally have it all removed. My stringers all look good but I would like to fill between them all with floatation before I add a new floor back to it. I see there is 2 lb. density and also 4 lb. density foam. If I were to use the 2 lb. does anyone know aprox. how much I will need to order to cover a area aprox. 9 feet long by 6 feet wide by 12 inchs deep? Appreciate any ideas.