Interested to see what you do with the back. I pulled my engine driven AC unit in my ambulance box. First off, it did not work--I had a leak in the custom 20 ft line from the compressor to the rear unit. Have you ever priced a custom 20 foot line? My ambulance came from Antarctica, and although had great fleet maintenance, they were not too worried about AC. Second, that poor factory compressor under the hood is taxed already keeping the front of my cab cooled in the Texas heat--it was not designed to run two AC units. And finally, the engine has to be running for the compressor to work, so the only time it could be used is vehicle in motion. I am installing a small window unit AC to run off generator or shore power. It fits in the space (mostly) that the original AC unit fit. I think I have it figured out, but have yet to test it.