If you want to mount it to the back deck. I would make a ported box and fire the port through the hole. I would also mount it a flush a possible to help reduce vibration, but I would suggest spraying rubberized coating first.
Jim NY Mets World Champions in 2002 2000 Black Contour SVT #53 of 2150 17" Konig Traffic w/Nitto 450 Borla Cat Back Zaino MB Quart and Shiva