Oh yes - we have here most Winters -15 C - and I take the vehicles into cold places, like eastern Europe, inside the Artic circle and up in the Alps - and we've had several times - 44 C in Lapland.. Going into Russia in 2 weeks to play with trains and it is a bit chilly there.
Going for bigger and bigger batteries that eventually will not get the job done - many years ago we started using engine pre-heaters that include warming up the interior and the battery itself. We run the heaters from a 2nd battery so the starter battery is 100 % ready for the job.
This helps a lot - the coolant is about 50 - 60 C, depending on how the wind is, and the interior is just fine. We sleep in them aswell on those trips and saves draging a lot of sleepingbags with you.. Engines usu. start on the button without pre-glowing.
Obviously, the initial cost of the heater is for many a thing but we find them to be well worth the investment.