For those nights where it gets below freezing but not sustained and cold enough to worry about above ground pipes but not worry about large m-a-s-s-es like the filter, has anyone thought of a tiny pump just to keep some water circulating? Something like a cheap 1/6 HP sump pump but with a suction line? Should be relatively easy to plumb it to inject into the suction side of the regular pool pump, throw a suction line in the pool, add a couple ball valves in the normal skimmer line and bingo, keeps water circulating through the pipes, pump, filter, etc, only at a very slow rate. Lot cheaper than running the pool pump all night. I like to think CHEEP!
Al