I have been storing a classic car and whatever motorcycle I happen to have at the time for 6 winter months in an unheated barn for 30+ years. My winter conditions are similar to golfnut's area. Here is what I do;
1. Oil change - You don't want all those nasty acids sitting in the oil pan for months
2. Full fuel tank - The less air in the tank the less condensation
3. Fuel stabilizer - I run the engine long enough to get it into the carb or injectors (Hey the stuff is cheap so why not?)
4. Disconnect the battery cable - I would rather have no power to the car than have a mouse chew through a wire and cause a short which might start a fire. Heat is a bigger enemy of a battery than cold. So long as your battery is in good shape and fully charged it should be good to go even after 6 months. If it won't start the car in the spring then you were due to replace it anyway. I have only had batteries fail me in the Spring twice in 30+ years and both times they were over 9 years old.
5. Floor covering - My vehicles sit on a concrete floor. I use some vapor barrier that is normally used for insulating a wall on the floor and park the vehicles on it. It also catches the odd oil drip from my 30 and 50 year old vehicles.
6. Breathable cover - Do not use a plastic tarp.
7. Mouse deterrent - I have never had a problem with mice but a friend had one last year so I thought I would try some Fresh Cab this year just in case. It's another thing I may not need but it's also cheap so why not?
Come spring I take off the covers, hook up the battery, make sure I have brakes, fire them up, and drive them home. The barn I store the vehicles in is a little on the drafty side which I like as it tends to keep it dry. Condensation from temperature changes is probably the biggest enemy of a vehicle in storage. Don't worry about how cold it will get, the main thing is you want a dry environment with a constant temperature.