This is a professional system from central Finland.
There winter temp is often -20C and reaches often -30C
The guy has a beekeeping company. He has now 1100 hives.
He manufactures HoneyPaw polyhives.
He keeps all hives in one box, because he limist the brooding to one box.
He fills the hive with syrup and it will last to August to April. He says that he cannot even go to hives before May because
forest roads have snow still.
The system is basicly common. No other trick are needed. Of course it is an advantage that you go and weight with hand what is the food storage in March.
This day is 2.2. 2011 and temp is -25C
inner cover has 3 pieces wooden fibre board, It is called "wind shelter board". bees wintering in finland