Mount a board to the seat back and hang it there. You could put it on the back of your sub box, but its easier for it all to get stolen that way.
-Ken V.
1998.5 SE Praire Tan Zetec ATX
psycho_bass@hotmail.com
Roush springs Roush rear sway bar BAT struts 17" Millie Miglia HT3 and a ton of subtle asthetic mods