This is an old thread, but the following info is still valid:

My guess is that he'll burn-out the cooling unit (compressor motor) in no time. It was designed for operation for short periods to maintain cooler temps, not for full-time cooling on hotter days, let alone being outside... Speaking of hotter days, it's at the warmest part of the day that the unit would likely fail.
No ventilation, warm-n-moist air sitting there...not even close to optimal.

MJ...are you still around and did you give it a try?
Rusty Trichome Reviewed by Rusty Trichome on . Working Freezer Cab Hello all- New member, long time grower. I recently moved from a cooler northern climate to a hotter southern climate. My cab that I keep outside, is getting too hot and I am looking to go in a different direction. I've read lots of threads on people using an old refrigerator or freezer for a cabinet, but I haven't seen anyone using a working one. All you need is a cooling thermostat, like this:Discount Hydroponics - C.A.P. Cooling Thermostat , plug the freezer into the therm, and your in Rating: 5