I'll have to agree with Shannon on this one.  As long as the plane is flown regularly, there shouldn't be any water to cause corrosion.  The basis for the heater assisting corrosion, is that some people leave the plane plugged in all winter.  If the aircraft is essentially in 'storage' with the heater on, yes you will have a problem.  I recommend using a timer, or just plugging in the plane the day before flight.  Having nice warm cylinders for a winter morning startup is a very GOOD thing.

   D. Story, ATP