I guess I would narrow it down to three simple rules for overwintering basjoos:
1. Keep them well insulated Build as wide and tall structure as you can afford. Hay is tried and tested, and is what lets' me overwinter bananas in Norway. Here, I use a structure of about 1 meter (>3 feet) in diameter.
2. Keep the clump dry Cover the structure with something that keeps the hay/insulation dry. A sheet of plastic tied around shoulc be sufficient.
3. Dont' uncover before stable spring weather has arrived. Insulation works both ways. If you have a day in February with 60degrees F, don't uncover the structure. Inside it will be nice and cold. Don't wake the sleeping bear! ;-)
