Trev,...picked up a Philips and Tempro (Same maker as the coolant heater, made in Canada, available at Canadian Tire) magnetic oil pan heater. It doesn't get hot enough to worry about it cooking the oil, but gets just warm enough to keep the 15w-40 flowing, though I'm considering 0w-40 for the winter.....
Instead of using 0w-40 for the winter, You might want to consider using 15w-40 synthetic oil, Amsoil's 15w-40 Heavy Duty Diesel & Marine Oil (stock# AME), it remains fluid down to -44°F or Amsoil's 5w-30 Heavy Duty Diesel (stock# HDD), it remains fluid down to -58°F. Both are good for year round use.
Amsoil Dealer #206107 since 1980
84 U 900
76 MB 4/94
79 MB 4/94 for sale
79 MB 4/94 parts truck for sale