My wife and I go to Arizona (from Illinois) for three months starting the middle of January. Unfortuneately, we have to leave our C6 back in Illinois. Does anyone know if I should be doing anything special to my C6, for leaving it covered for that long without being started, etc....

If it is stored in a dry place, I would just disconnect the battery so there is no chance of fire. Don't forget your key, you will need it to unlock the car and open the hood up to reconnect the battery.