My solution was to shove one of these in the footwell. Fits perfect and I can have the whole thing out in 5 minutes and very little weight gain. Not going to win any sound contests but it does the job. I also replaced the hu and speakers too. All of it combined made my system as good as it needs to be.
I am pretty happy with my setup - Pioneer P6000UB, Eclipse 4" and 5.25" speakers, Ipod Nano, and the sub listed. Cheap and simple.
JVC CS-BB2 Compact powered subwoofer at Crutchfield.com