I have my diesel plugged in to my garage on a timer. It comes on at 4:30am so when I leave at 7:00am the truck starts easy and heater is slightly warm. I have seen a 12v heater, but was not effective. We I was younger I use to spend alot of time in Loa utah with the brown brother construction co. My job was to start bon fires under the d-9 cats to warm the oil pan. You might try that.
