Storing Dry Rubs

What's written here will be pretty obvious, but still I make these mistakes all the time so it bears repeating...

1. Store rubs in airtight containers.  Rubs are mostly salt and sugar, both ingredients that will absorb moisture and cake or clump.  Use containers that seal well with rubber gaskets or tight fitting lids.  I always forget that the soup containers from the takeout restaurant have holes punched into the lids. 
2. Use a container that is appropriately sized.  Don't put a cup of rub into a quart container.  Even if it seals well, you've just locked enough moist air into the container to clump up the works.
3. Glass or Plastic?  This is difficult because both have pros and cons.  Plastic containers are light weight, don't break, come in a variety of sizes, often stack well and can be written on in marker.  Glass containers won't absorb the smells, tastes or colors of rubs and are see-through.  I use both.  If you think a plastic container will impart flavors to a new rub, fill it with white vinegar for a few hours and rinse.  (Keep the vinegar.  You can use it again, or put it in a spray bottle to sanitize your kitchen surfaces.)  
4. Make sure the container is dry!  Nothing is worse that dumping a rub into a jar to realize that there was a little water in the corners, and not your rub is stuck there.
5. Label your containers!!  Really, I can't put enough exclamation points here.  This is my major sin, and I commit it over and over again.  You would think that once one has coated a piece of pork with the cinnamon cocoa powder meant to coat the chocolate truffles, one would never make the labeling mistake again, but apparently not.