I probably had too much time on my hand. This is what I did to store my summer wheels/tires:
1. Wash and wax, then double-bagged
2. Store in basement, stack them flat, one on top on another.
3. After 1-2 months, reverse the wheels so that the top one will go to the bottom.
You see, I bought some new AMG wheels last summer and I am doing my best to keep them in top shape.