The 6.5" Kicker sub has been done a couple of times. Check out these threads. This will be my next project:
http://www.elementownersclub.com/forums/showthread.php?t=51793&highlight=kicker+sub
http://www.elementownersclub.com/forums/showthread.php?t=54084&highlight=kicker+sub
http://www.elementownersclub.com/forums/showthread.php?t=51793&highlight=kicker+sub
http://www.elementownersclub.com/forums/showthread.php?t=54084&highlight=kicker+sub