Engine Heaters

I use an Aerotherm Deuce .  I like that it has its own thermostat so I just hang it on the prop hub, set the temp to 60 (or whatever) and irate will keep the engine at that temp.  You do need to ensure the tubes fit the cowl inlets. It  fit fine in my Sting S4. 

Look at EZ Heat. It’s a heating pad applied to the oil tank and crankcase for under $200. Have mine hooked up to Switcheon and controlled with my phone. Has worked great for about 10 years now.

The gold standard for good engine preheater is Tanis. They make a system designed just for the Rotax and it heats everything and not just some other system that a heater Mfg tries to make work on different engines. They also Mfg other heaters, but they are specific to those engines. 

I've installed a number of these and talk to owners that have Tanis heaters and they all like it and no negative comments.

Ones like Reif and some others just don't do as good a job to heat everything. Some engine heater Mfg's only put a pad on the oil tank and one on the bottom of the engine like Reif. That isn't near a good as a Tanis. Plus you can buy an electrical plug that you can activate or turn off using your phone. For example if you want to fly some cold morning you could call the electrical plug and turn it on the night before or whenever. But let's say you wake up in the morning and decide you don't want to fly so you can call the plug and turn it off. I see so reason to leave a pre-heater on 24/7 and never turn it off.

I love and use a "Twin Hornet 22" whole engine heater here in very-not-warm Michigan. It's largely used as a bilge heater on boats and is therefore rated for use in wet and potentially explosive gas environments. Its very long cord, heavy duty cord is a safety plus too. With limited power, 250W max, it takes some planning to do a thorough job on very cold days, but a SwitchEon unit lets me turn it on from home, or program a time in advance, or have it come on based on temperature.

https://www.aircraftspruce.com/catalog/eppages/aircraftheaters_08-12217.php