Inputting subs

How can I fit subs into the back of a 90 camaro without spending too much?

I built a sealed enclosure that fits into the bottom of the hatch area of my '85 Firebird SE and again for my '91 Firebird that will hold a single 10" sub. I called it the F-Box (http://www.fbodyaudio.com/cgi-bin/yabb/YaBB.pl?board=3rdgen;action=display;num=1038617226 ). With only 150W of power connected to it it hit harder than my current dual 10" Stealthbox setup does now. I used to demo it for people and their jaws would hit the floor when I would show them that I only had a single 10" in back.