I just got a Kat's stick-on heater pad from Amazon for the hydraulic pump on my snow plow. Hopefully, it will get the hydraulics warmed up enough to work when I start out. Once it gets warmed from use, it is OK. Kat's makes all different sizes of stick-on heaters that could be used on the diesel fuel filter and the engine oil pan. In my situation it helps to use Meyer hydraulic fluid in the plow. It seems to work better in low temps.
I have been using a paint stripper heat gun to warm the hydraulic pump. It looks and works like a hair dryer only it gets hotter. It is probably just a little safer than coals under the truck.