We are in our eighth and likely last winter of running a group of half to a dozen colonies in the high desert Rockies- 38 N, 7500 feet above sea level, most of them in the middle of a wide valley with a dramatic temperature inversion in the winter, lows below 0F common, -20s, -30s occasionally.  Considered drilling ventilation holes in the top boxes the first winter, but skipped it and have since then tried to run the colonies fairly airtight with minimal openings.  The equipment is 8 frame, in good shape, lids are plywood and on top of that polyisocyanurate boards, then a contraption that can serve as a bottom board or top cover, and sometimes styrofoam boards above that, below lids.  The bottom boards have an opening of a nominal one inch determined by the side boards, maybe 5 inches in length, block inserts in the winter reduce it to an inch or less.  Learned about mice the first winter- one plugged the reduced entrance and the colony was not able to fly.  Since then hardware wire mesh is tacked to the entrance until the first pollen (mid April).  It is dry up there, but I have not seen ice buildup, condensation or mold below the lid.

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