You can fit a 2 gallon tank in the trunk if you move some stuff around. Here is a quote and pics from a thread I started a while back.
Originally Posted by SRTpowa
Well I just had a major breakthrough on this project. I decided to get medieval and rip the styrofoam out of the rear corner. You have to take off the panels to do this and could be done without breaking it but I had already drilled into it, so I just man handled it out piece by piece.
Anywho, the good news is I discovered a fairly large area beneath it to locate my pump and reservoir. I should have done this before I drilled my holes but oh well I'll make it work.
There were some electronics in the area that I relocated to a cubby hole behind the wheel well. Not sure what they are for, but one said this side up, so I bolted it accordingly to one of the rear tailight bolts.
This is good news for those wanting to keep their trunk space like me.
Pics are below.
My car ran like crap before this mod, I.E. supercharger not engaging half the time. With my IC system it always works now and I have the ability to super cool it by dropping dry ice directly into the tank. I have tested the dry ice once on the street and it seemed to work great. The coolant was chilled to the touch and the car pulled stronger on the street. I have yet to test the dry ice at the track, but next time I will.
Here's the video I made when I finished it. I have made a couple small modifications to eliminate the kink 3/4" in the pump feed hose and sealed th tupperware with silicone.
http://www.youtube.com/watch?v=lefNz407oeg
It's ghetto but it was cheap and it allows me to enjoy my car everytime I hit the gas now. The concept is there I just need to clean it up I suppose.