I mounted mine under the rear seat behind my sub box. Then I was able to use the amp power to connect the compressor and stay within the distance to a power source as firestone rcomends. I looked at using the back bed box but it wouldn't work. Plus mounting it this way I only needed one hole in the firewall instead of a bunch or a much larger one.
http://www.titantalk.com/forums/362280-post78.html. Here is a link to my compressor and controller.