I've got an interesting idea for an amp rack as well. I'm going to link my 3 Rockford amps together and mount them on the gas tank but at about a 45* angle so that they stare you in the face when you raise the hatch.
I've got 2 Audiobahn subs coming soon. The shiny ones. Don't worry, I didn't cheap out, they are blown and I intend to cut the cones out and use the shinyness as speaker grills. Cool idea, huh? I got them for 5 bucks plus $25 shipping, so I couldn't pass them up. They will be covering my old Image Dynamics IDQ12DVC subs. They are awesome, but lack in the looks deparment with an all black cone.
Anyway, behind the amps will be an enclosure that holds the PC, Alpine H700 brain, passive x-overs for the fronts and other misc stuff. There will be plexi windows and lights with lots of raw circuit boards showing. Should look cool from the front looking towards the rear. Then from the rear looking forward you'll see all the subs and amps. I like it.
I'm going to pull the rear seats out and make storage bins there as I carry a lot of junk that I use for work. I have to put it somewhere. I'll probably leave the heatsinks exposed to keep things simple, although I could remove the back panels and mount fans to circulate the air. I have to come up with a filtered crossflow air circulation system anyway for the PC.
I did a photoshop of what it might look like from the rear. My car is black, but otherwise it's the same.