I live in Arizona and we get over 100 inches of snow so I understand puttting cars like the Xfire and Porsche away for the winter. Surprised about the amount of snow? Besides what others have said I would add the following:

1. Check the owner's manual it has info on what to do for storage.
2. I make sure my leather seats are conditioned.
3. I put a Yankee candle air freshner. Leather scent in the car.
4. Since I have dogs, I have some sacks of a rock stuff which removes odors. I put one in the trunk and on the floor of the cockpit. I forgot the name of them. If you are interested let me know.
5. I took exterior plywood and cut it into 2' x 3' pieces and covered them with indoor/outside carpet. This seems to have worked to end flat spots on the tires.
6. My cars are stored in a heated garage so the temperature does not get below freezing. BUT I do make sure I have conditioned the exterior black trim around the windows, tires, etc.
7. I cover both my cars with a car cover.
8. In my state (Arizona), I only keep comprehensive (fire and theft) on the cars so I go to the Motor Vehicle people and sign a statement that says I will not drive the cars until I put liabilty insurance on them. This allows me to keep my plates. Check out the rules for your state. This is super easy.
9. I never set the parking brake.
10. I start the cars every 2 weeks. I use a different key fob each time on the Xfire.
11. I do not lock the cars.

Hope this helps. Do a search and I am sure you will find other suggestions.