My general rule of thumb has been if half the day is going to be 40 or above, I don't worry about a thing. Run the furnace and maybe open the cabinet doors so heat can get to the pipes. If it's going to be highs slightly over freezing and everything wont get a good chance to thaw during the day or if it's going down below mid twenties overnight, I'll use a well placed small 1500 watt heater and disconnect my water lines overnight. Camp often in Oct, Nov when night time lows are in that range without issues.
