The moisture of give comes from respiration of bees.
When bees consume 25 kg sugar, it generates 10 kg water.
The winter cluster is warm (23C) and respiration air will condensate onto cold surfaces.
When the space of cluster is small, the condensation point goes outside of hive and the hive will be dry.
Fast bottom and a small upper entrance is very good.
If you have mesh floor, it need not upper entrance.
I tried mesh floors and noticed that it consumed 50% more food than fast bottom. It depends how windy is the place.
Bees must be in fresh air over winter. If you have a shelter, where is no wind, bees are easy to get nosema.
Many over winter bees in cellars. The temp must be under 7C, dark and electrict ventilation.