Both Vehicles (2012 Jeep GC and 2003 Ram) where plugged in all weekend as it was -40 with windchill this Am and it helps alot.......Truck also has a battery blanket.
I could tell some long winded stories about No Oil Pressure, Oil change lasting only 3 weeks etc, Power steering pumps, Brake calipers, exploding brake shoes but it comes with the climate I live in. General rule is if its gonna drop to -20 C or lower they get plugged in. At work my employer provides outdoor plugs and extension cords for every person or POMV.
So unless you get -4 F Temps or colder I would not Bother! Danny
Edit: If You do it is easy to Install. Mind you I have a 5.7, but its a dry fit assy that goes into the Block just behind the starter and has one Bolt. The cord is then Plugged into it and is then tied and directed towards the front drivers side of the vehicle and to where ever is convenient. Mine is tied into an outdoor cold weather flexable plug thats tie wrapped to my front Tow Hook Assy. Cost up here is about 55-90$ from the dealer and replacement cords run about $25.
All or Most (Some Mitsubuishi's argue about -50 Start-Up) Vehicles sold new in the Canadian Market come standard with a Block-Heater.