Mr. Ben, I live North of you: North Arkansas and I leave in my screened bottom boards all winter. The bees seal the top cover so there is little draft,,,,, sometimes to little draft. I did lose one hive to condensation last winter.
The hive that died out had a huge cluster, much bigger than my other 19 hives. The winter cluster was so big they generated more heat, thus more condensation. By the time I discovered, in Feb, the winter kill, it was to late as the cluster was wet, very damp and frozen. I was sick I tell ya. This dead out was my only Carniolean {sp?} hive, just a beautiful black, gentle bee that supposedly is known for small winter clusters and late spring start up.
So the dead bees were clustered, all huddled together, plenty of food as there was no dead bee head first in cells. The beautiful solid black queen was in the middle of the cluster. I think next year I will purchase another carniolean queen, they are just a totally cool beautiful black gentle productive bee.
Point is, screen bottom boards may or may not produce draft. With this one hive, out of a total of 20 there was not enough ventilation. Go figure???