I saw a question about air conditioning a camper shell for dogs. The answer was to let the dogs ride in the front.
I am looking for a way to A/C my camper shell as well. I have a heavy duty alternator in my pick up.
Several companies make a 12 Volt DC powered air conditioning unit for truck cabs that can be powered from an alternator charged battery. They are not cheap and they usually require adding a heaver dual battery power system, but you can buy these.
I think you will find the cost will be so high that its not worth the trouble, but give it a try.