Some one mentioned the difference between maintaining them on a bike or off in storage. That is important, as off-the-bike conditions are often less weildy than having to work with them while still installed on the bike.
I think someone also mentioned that cold temperatures are damaging to rubber. I would only agree if the rubber items in question are exposed to daily use. However, hoods in a ziplock baggy protectively stored in the back of the freezer has worked fine for me going back to '87, (damn, that seems like a long time ago!). Just let them gingerly thaw out before you start banging them on the table or other injurious actions.
If you really really want to make sure of their longevity, give them a nice coat of liquid latex before you store them in the freezer. Cheers, Dave Anderson Cut Bank MT