It gets a bit chilly here in Colorado at times. So I picked up a Kat's 24100 100 Watt 4"x 5" Universal Hot Pad Heater to adhere to the bottom of the oil pan (on the left side only). This is not my idea, as others have done the same. I recognize it's a bit of a risk to 1) fly with it as it could come loose and catch fire and 2) unattended heating when on the ground could also go awry. However, in the case of point 1, there is a lot of precedent for this method, so I'm not worried. And in the case of 2) as with all things in my hangar, my rule is that nothing gets operated unattended.
I used RTV to seal around the edges to help keep the adhesive isolated from contaminates. I was careful to route the electrical cord in such a a way as to minimize vibration. And I used an additional EA LV-1 Heat Shield to protect the cord from the exhaust pipe. As of this writing, it's survived 5 hours of flight.
When plugged in, it only takes 10 minutes before the whole oil pain is toasty warm. On engine start, when the oil circulates, it surely gives up a lot of its heat to the engine case.
Here's an oblique view looking up and back.
Looking straight up. Forward is the top of the image. You can see the additional EA LV-1 Heat Shield adjacent to the one protecting the throttle cable.
