The temperature in a closed car gets much higher than the outside if there's any sun at all and that's the reason I don't keep my nice film cameras in the car. I firmly believe that many camera repair problems stem from being exposed to high temperatures in a car or an attic.
The problem is I miss out on a lot of good photo opportunities by not having a camera available. I do have a nice little Rollei 35S which can fit in my pocket but many times I wish I had one of my Nikons.
It seems to me what would be ideal is a way to keep the camera at "normal" temperatures, say 60-80 degrees F. That way bringing it out into use would not cause any condensation problems. I'm thinking perhaps an insulated bag and the cooling device (frozen water bottle, gel ice packs) in an separate insulated wrapper to slow down the heat transfer. It would take some experimentation to get it right.