I'm with nutcutlet on the 'right up against the house'. Just check the pots for moisture (occassionally). The eaves and walls of a house can be quite a 'rain shadow'. Unless your house has extremely efficient insulation there will always be some heat leakage. A south facing wall (if not shaded by anything) will capture whatever winter warmth there is from the low sun.
Problems I've encountered when overwintering 'hardy' plants in containers hasn't necessarily been with sub-zero temperatures. Low single figures plus rain can lead to prolonged waterlogging of the compost in containers (dependant on compost, container type and any drainage 'enhancements). The roots start to rot, and that is a very good way of killing off any plant