I remember a while back somebody was trying to quiet down their boat. I used sounddown 2 inch foam under my deck of my wheelhouse. I went as far as to double it up using 4 inch spike fasteners. I also installed a 4 ft. 2 stage muffler from centek. MDI45 helped me configure it. Once everything was fit in, I glassed in cradles to support the muffler. It did wonders. Ill include some pics when Im at the boat if anybody is interested.