As AH says, I probably wouldn't for short periods below freezing. If you can plug it in to shore power (mine is sitting in my driveway, plugged in to a 15A outlet outside) and put a small draw electric fan heater in it, that would help.
2018 (2017 Sprinter Cab Chassis) Navion24V + 2016 Wrangler JKU (sold @ ????) - 2016 Sunstar 26HE (sold @ 4600 miles) - 2002 Roadtrek C190P (sold @ 315,000kms)