Hi Folks
My son used a car heater that can be purchased at most hardware stores. Place it next to the firewall clear of anything that could possibly catch on fire. Cover the engine with a blanket. Most flying schools use blankets and can tell you where to buy one. Set the electrical timer to turn on the heater approximately three hours prior to flight. Make sure that you take your heater and blanket on your flight and plug it in on any stops longer than an hour depending on the outside temperature. He never had any starting problems and the preheat extends your engine life.
He also had wing and tail covers for the real nasty weather.....