I would recommend the cooler/case idea also. There are too many variables in the backseat of a car; breezes, humidity/temperature fluctuations; a nice small styro cooler would help insulate against that stuff. Do you plan on using air conditioning in the car; if so, you might even need a few heat packs.. but then again you don't want to cook the snake. I would do a dry run; start up the car, put on the AC, get the cooler all setup and put in some heatpacks and measure the temp they get into with the cooler sealed up.. if it goes over 90, remove a pack, etc.