What Sue says covers it all. Our diesel starts fine at minus 20 Celsius without plugging in, below that it protests... we have to run the genset every morning anyway to charge batteries when furnace runs all night (we have double 6 volt batteries).
Sue's suggestion of Liard Hotsprings is great you will love it.
If you decide on coming as far north as Whitehorse (and we think you should:)) there are camping opportunities for you to check out such as here:
Takhini HotspringsWe can come up with other options for plugging in but most campgrounds are still closed.
It can get cold as in minus 40 at night but days warm up as sun is higher by then.
Take booster cables and good luck!