Never once plugged mine in and it starts every time. Proper seasonally adjusted fuel is the key to starting any diesel. Whether you're in Alaska or Antarctica.
I thought you were in Florida?We hit 0 this morning (F) and I plugged in Old Nelly and she started fine. The advantage of the oil pan heater (for me) is that it seems to blow heat a LOT sooner than if I don't plug it in. Going to hit -10 (F) on Friday night, so I will see if plugging in makes a difference.