It probably will crystallize as it freezes, but that should undo itself as the bottle warms up. Your biggest concern may be with the bottle. Many liquids expand when frozen, and that may burst the bottle it comes in.
I know it gets cold in Wyoming, but does your mail have time to freeze?
I left mine out in the weather for a good six years. It is in a glass cough medicine bottle. During that time, it faced temps as low as 0 F. It didn't freeze--at all. No crystallization, no nothing. Remained liquid as far as I could tell. The bottle remained intact.
I wouldn't recommend doing the same though, simply because plastic containers or plastic tops will deteriorate quicky if exposed for prolonger periods of sunlight. UV radiation breaks plastics down. I just wouldn't worry too much if you forgot the bottle over a winter, or two...