I've been using pipe insulation in mine. If you have the room, you can use pool noodles and cut them up to fit. Any of these can absorb water and oil over time to it doesn't hurt to put new ones in yearly. Some people use bubble wrap to put in some areas where it will fit. Ifyour boat has a hatch or some kind of cowling, add some sheet foam or whatever else you have in case it comes off in a flip. Double-sided tape will hold that in place.