Question about rubs and refrigeration

Hello!

I wanted to make my first meat rub, starting with a foundation of lime flavored sea salt.  I had read that a good ratio to use is a cup of coarse salt to the zest of two limes.  However, do I need to refrigerate such rubs if they contain moisture-rich ingredients such as the skins of fruits?  I am concerned about it growing bacteria or mold.

Any advice would be appreciated.