I used one when I had my boat. What I did was used a bit of coat hanger wire and put it on top of a deal like this: http://www.boatersworld.com/product/338260060.htm
I also opened up all of the enclosures in the boat so that air could move around. I also put one of the dry air blowers in my rear locker.
Then on the side of the motor's block, I put a magnetic block heater.
Boat never had a bit of mildew and other than doing the quick block drain (just opening the thumb screews and letting the water out) I never winterized. Living near Seattle it does not get too cold but does stay damp and wet all winter.