The Volt will only attempt to maintain the temperature of the high voltage traction battery between 40F and 60F when the Volt is plugged in. This will do nothing to condition the 12V battery so the 12V battery might end up freezing in extreme cold, not be able to start up the Volt. If you leave the Volt parked, powered on, the Volt will automatically shut off in 2.5 hours to prevent the possibility of the gas engine starting up unintentionally. When parked inside a garage this could cause a dangerous build up of carbon monoxide.
To circumvent this, there are a number of ways; easiest I know of is to use a large elastic or clip to hold the gear selector button in, (as if you're about to pull the stick out of park), and the car doesn't turn off bc it thinks you're in there holding the stick.
This trick worked for my 2012 Volt, I don't know if it'll work for your 2017.
The HV battery is very well insulated so it'll prolly be fine, but the 12v one in the back of the car may be more exposed.
Saving charge for when you park overnight with it left on is a good safe bet IMO.
I have camped overnight in mine in the mountains here, not as cold as your trip though, and over 5 hours, even with the heater on, the ICE only came on 3 times for around 90 seconds each, using about 300ml fuel. (Whatever the conversion is)
Good luck, let us know how you go, make some videos