I typically don't leave inner tubes unused for a number of years. I thought though that rubber had to be used in order to stay pliable (?).

I do have experience with 2 bikes that were given to me (to give away to a local charity called Bike Again) for me to refurbish. These bikes had been sitting in a garage or basement for 20 years or more that had dry, crack tires and tubes. I was able to pull the valve away from the tube very easily, and also able to pull the bead off the tire by hand.

Sure, a few years would cause no trouble with a tube or tire, depending on the circumstances. But an extended period of time would most likely. As stated, jusdt use some common sense with storage.

In short, I wouldn't worry too much about the storage of the tube(s). Both are relitively inexpensive, that if left sitting around for a long time and suffered damage, then they are easily and inexpensively replaced.