Xerox, I have used pennies years past, but not at random. When I can actually see condensation. I tilt my hives, I use burlap and fondant on a 3 inch wither board on my best queens of desired genetics. On warm days, say 65F, I will remove the top and check on condensation and stores.
There are time of extreme cold that my bees don?t like ventilation. Determined by bee propolis to close off vents. So, in short, condensation and food are the main concerns. My bees can tolerate single digits but not water dripping in the cluster.
I believe your state, Washington, is much warmer than Arkansas: single digits, rarely below zero F. Is this correct?
Blessings
Van