It's fairly simple to build a rack out of 2x4 lumber, stowing the tires with or without wheels fitted vertically. Best for the tires, and easy to mount on a wall somewhere (garage, basement, mud room, whatever), making it easy for you to load/unload them.
You can even leave the rack outside, use a chain to run between the tires/wheels for security. Cover the chain with PVC if there are concerns about scratching the aluminum wheels.
Tire Rack sells metal racks if you don't want to save a few bucks or are unhandy. They also sell covers which do help, insuring no UV-related degradation for you. Tires do cost money, no point in letting them rot for no reason.
It's what I do. From experience, if you can, make room for more tires than you need right now; once you have good storage you tend to use up all available tire storage.