I'm here in Va, and it gets very hot in my minivan during the day even with the windows in the back slightly opened. It is impossible to leave anything electronic except for the GPS in the car. I keep Costco freezer bags in the car for shopping, but even those can't handle the heat on very hot days. The best advice is to carry your camera with you in a small bag, or holster. It's not awful, and how much gear do you carry around anyway? I only keep my 5D2 with 24-70 with me most of the time. That I can carry in a holster bag or my Domke F-5XB. Not much weight. If I go to a shoot and have to wait, I just take a few larger bags with a wheely thing. Jon advised this years ago and I still use it. Not too glamorous, but I don't care. I can't leave such valuable equipment in the 120+ temps in the car.