I run methanol And I have a Moroso heater in the pan and two block Heaters in the block. You'll really appreciate them when the temp drops below 60 degrees I can plug them all in and get the motor up to 100 degrees in about 1/2 hour. They also shorten the warm up time as well.
I have had no problems with oil sludging in the pan but I've never left them on overnight.
If you put a vacuum pump on it you can eliminate the "milking up" the oil too.