Well I've camped in those conditions, in a tent, without a California. It's an experience
I also saw a lot of vans (VW, Ford, Renault) that started just fine in -30. Perhaps they get some special preparation and additives, and extra insulation around the car battery can also help.
I believe that having the petrol heater on will make a difference. Heat will leak towards the engine and battery compartment, and it will make a slight difference.
I haven't been to Levi (finnish lapland), only to the norwegian/swedish border. It 's not snow and fir trees all the same. There's great mountains, snowy landscapes with lakes, beautiful views and some of the most stunning desolate roads. The road from Kiruna to Narvik is just wonderful. A must see IMO.
You can make multiple day tours (on foot with snow rackets or skis) and sleep in swedish cabbins.
I was just wondering if the engine would still start after a couple of days in the cold.
How much diesel does the heater consume anyway? I guess the answer is "it depends on the conditions", but I have no idea now..