They must be stored upside down in a climatically controled environment under armed guard.

Naw, lad, I just leave 'em in the box and toss them up on the self until I need them. Usually within a year. I'm sure if you left them for a number of years they would get "old" and unreliable.

Store them using common sense; away from a heat source, don't leave them in the back window of your vehicle, or store them in a damp place. Cool (room tempreature) and dry place.

During their time in my seat bag I will put inside an old sock with some baby powder. Sock protects them from chafing and baby powder keeps them unstuck.

EDIT: Oh, they say that rubber should be stored away from electric motors.