I may go overboard, but I just finished the water line winterization. I have a compression which I limit to 40psi. I hook it up to an in-line filter just to capture any oils and such then begin the process. It usually takes me about 1 hour until I am completely satisfied that ALL the water is gone, however I'm certain I am over doing it because after 10 minutes or so, there's little water coming out, usually just mist. I doubt that the mist would cause any issues with freezing, but I run the air until it's completely clear.
Other than that I would put a gazillion mouse traps in there just in case! I have 6 setup and have caught 2 mice.