I've been mixing them into pint size Mason jars, then I use my vacuum sealer attachment to seal the jars, then they go in the freezer.
I usually end up using a cup or two of rub on bigger cooks so I just pop the jar open, transfer what I need into a shaker, then reseal it and put it back in the freezer.
Not sure if it's worth it or not, but my rubs with brown sugar in them have not clumped since I started storing them this way. Before I did this, I regularly had a brick of rub in the jar...