If you want them to stay in good condition then inside wrapped in plastic...Extreme temps will deteriorate...

 

I put my stock rims in the box that my new rims came in. Though I guess I should take the advice of folks here about the temp and moisture control environment. They were in the house for last winter, but I moved them into self-storage for the summer. THey're back in the house for this winter because I'm thinking of throwing them up on eBay (dreading the shipping cost though).