Best Before Date on Tubes

[Eugbug]

What's the shelf life of a tube if its stored in a cool, dry, dark place?
I'm just wondering whether stocking up on tubes is a good thing if they are going to be stored for a few years.

[nfmisso]

Oxygen and UV exposure kill rubber. Moisture has little effect; in fact storing them under neutral water will keep most the oxygen away from them....

I would keep more than you need in a year. What happens if you change tire size?