My friend is interested in getting one of these:
Small Volume 12V DC Tiny Compressor for Air Conditioner Refrigerator | eBay
At first, I was kind of skeptical about a battery powered vapor compression system. I know it's done, but at what cost! These little compressors look like fun, and maximizing their efficient use would be quite the challenge. I would think you would need two in parallel, for your application. Two DC compressors could be quite handy, since capacity could be varied by reducing their speed, and/or by running just one or both! Kind of spendy though!