Years ago I bought a Kat's magnetic 110v heater.
It will stick to oil pan easy, it makes starting anything out in the cold like a hot day.
Comes in really handy sometimes to get stuff running.
This is the kind of heater you need to warm up the oil anyway. Most block heaters warm the coolant which helps starting (especially on diesels) and reduces wear but with the oil hanging in a sump below the block there's barely any heat transfer to the oil that way.