I've tried every method myself. If there is moisture in the air and temps are cold enough, sometimes a top crusting or frosting is inevitable.
Buckwheat Hulls work well, but even they will crust over after few nights. So will all forms of dried dirt (salted, calcium added, waxed, etc.) I have had pretty good luck with coal ash, but it too needs some maintainance work after a couple of nights in this region of Nebraska.
I just make a point to check things over daily. I use a small, sharp stick and poke into a spot in the bed away from the pan. If I can push the stick through easily, then 9 times out of 10 the trap may still fire that night. If I get resistance immediately from a frost crusting, then I will pop the trap and rebed in dry material, and then I am good to go for another night or two, or until moisture is present in the air again.
Freeze-Thaw conditions (warmer by day, cold by night) are tough to keep things functioning in. So are the extreme cold conditions. I deal with freeze thaw by placing my sets in the shade so that they never get a chance to thaw out. As for the extreme cold with moisture in the air, just be diligent with the set maintenance and have plenty of dry or moisture-proof material on hand for remakes.