It has been extremely hot here in Texas so I have been keeping my opossum indoors. I'd rather allow her to be in her large outdoor cage which she is used to, so I have devised an air conditioned nestbox for her.
Basically I took an old thermoelectric portable cooler, cut a hole, installed a cat door and then added a thermostat to keep it from freezing her. Very simple concept in the end.
The thermoelectric cooler can keep her up to 30F cooler than outside temperatures and it only draws 150 watts in the end when running. I think that a switching power supply will be more efficient too so I will report back with stats after all is said and done with this project.
Right now she is not trained to use the cat door, so that will be a make or break for this, but I think that she is smart enough to get it quickly.