Don't freeze. Dark cool area like others suggested.
We buy rubs in 5lb bags and snip a corner. We pour out what we will use for a cook, then place the 5lb bag into a food saver bag that we purposely make about 1 foot too long. Vac seal and store. When we need more rub, we cut off the top portion of the bag, just under the seal. Take what we need and reseal. We usually get about 12-15 uses out of that one vac bag.
Crash - HIBarbeque.com