Who has overwintered deciduous container trees/shrubs in this way?

Obviously the idea is to keep the rootball from freezing too deeply...but I have questions:

1. Do you have some sort of heat? If so, do you keep it above freezing at all times, or do you find a few degrees below is not harmful?

2. On WARM, sunny winter days, does it get warmer (just from solar radiation) inside than out, or does it typically stay somewhat cooler? My concern is that a warm spell might be even warmer inside the building, and cause budbreak at a time the plants can't be moved outside to sunlight yet.

Would insulating the structure moderate temperature extremes on BOTH sides of the spectrum?

Would any sort of automated ventilation system be helpful, such as is used in a greenhouse?