Wind may be one of the biggest issues you face. Nothing chills a hive down more than having -40 degree air blown into every crack and opening. In Vermont, we used those black corrugated hive wraps and they were life-savers for the bees. If you can't find those, black roofing paper, stapled on the hive like a big black present also works great, and breathes well so the hives don't get too moist on the inside, which can lead to water condensing on the cover and dripping onto the bees.