I have a couple I only use now and then, but need to be able to start on a moment's notice. If it's below freezing, I just leave them plugged in, but that's only part of the picture, so I just bought a couple of trickle chargers so I can keep the batteries up, too. They fire up like it was summer, and don't take as long to chase the frost off the glass, either. Considering none of them are under 100K miles, babying them seems to work pretty well.
Twenty below, static air, this morning (-43 wind chill). Some times it's nice not to be out on a drilling rig. 
This is just an old plastic toolbox thingy with a 10ga pigtail coming out of it... inside is a smart switch tied to a 110 4-way that goes out as 4 12ga pigtails... Also with a manual override to the smart switch... all pretty waterproof and bulletproof...
That runs a trickle charger/exerciser or batt blanket, an oil heater, and a block heater - all standard, hard-wired equipment on a Northern pickup. I won't leave it plugged in unless it is getting past 15/20 below... Thought of building in an electric heater for the cab too, but right now, I don't think I have the amps for it.
If it works right (which I can't tell yet for sure), I have a 30amp RV receptacle for plugging into shore power, which is normally doing nothing... I'll run the whole works off of that before it's done. For now, my dumb little box will do... I am pretty proud of it.
I ain't much for smart features on my house - Don't get me wrong. I know better than most how easy it is to hack things... But there are a few things that would be mighty handy - This is one of em. Porch lights and flood lights would be another... a light out by the highway for the pizza guy... who cares if someone hacks those things?
When I can stand by the window with my coffee and watch the light come on in that little box when it's way below zero... well that just gives me the fizz.
