Kosher salt is much more reistant to moisture and clumping than iodized/table salt or pickling salt.

I keep mine in an unsealed container on my counter right next to all kinds of moisture sources (cook top, microwave, etc) and have never had an issue with moisture messing up my salt. I usually keep about 3 cups worth so it sits for quite a while before being refilled.

The box sits in my pantry unsealed too and I've never had it clump or turn into a salt lick.