I almost hate to muddy the water on this topic, because living in Wis I will probably end up with a heater. But from the aircooled engine world of airplanes, the concern with extended operation of a heater that only heats the crankcase, moisture is driven out of the oil in the crankcase and condenses in the unheated cylinders - potential for corrosion. For the plane, I run the heater for an hour, for the tractor, I will probably do the same, with a timer.