Gary I have run the air cooled Peltier fridge at -24C when it was 1C in Melbourne. The darks were very dark and the Canon was none the worse for wear. With my method the camera cools down quite slowly and once the Peltier fridge is at 0C the interior of the fridge is bone dry as all the water is now frozen on the cool side of the Peltier heat exchanger.
I am sure the camera can handle -30C. Even at this temperature the sensor due to its own heating is at -13C.
I have ordered a radiator
http://www.pccasegear.com/index.php?...ducts_id=13082
and with two 120mm fans will easily cool the coolant down to nearly the fridge temperature.
I am going to use a pressure cooker as the reservoir to stop water from the anti freeze evaporating/sublimating and frosting up the cold metal bits inside the fridge. Its just a matter of drilling and tapping a couple of holes to take a 1/2" barbs
http://www.pccasegear.com/index.php?...ducts_id=11196
Bert