I'm planning on attending a graduation in a couple weeks and I'd like to keep my dog in the back of my truck IF I can find an air conditioner. I have a camper shell, and tested the fan blowing out the window today while at work. It was still 90 degrees inside- too hot. I see all sorts of gimmicks out there, but wonder is there a good 12 volt air conditioner I can put in the window that doesn't cost an arm and a leg? Thanks