This sounds like an incredibly complicated solution to a nonexistent problem. You've got a couple of hundred horsepower available to run a compressor off the crankshaft, and plenty of technology already in existence to get that van as cold as you can stand. Just get a regular automotive AC system working, and drive on! I've been installing and/or repairing automotive systems since 1959, and they're not that complicated. Adding a second evaporator back in the van is simply a matter of running a couple of hoses down the frame, and mounting the evaporator with the necessary fan speed and temperature controls. Charge it up with R-134, and chill out!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!