satuja
Last night we made a test sleep in -18 degrees celcius in our GC680. We have not put water in the tank yet because of the cold weather here in Finland and haven't used the toilet either. We wanted to know how the temperature is inside compartment where the toilet cassette is to be sure if one can use it in winter. I put a ruuvitag bluetooth temperature sensor (https://ruuvi.com) with tape into the side of the cassette and placed the cassette back into its place.
Outside temp was -18 and inside the car was +12 according to the control panel in the back, and the cassette was -2 after several of hours of driving after we parked for the night. Time was 19.00 when we started the diesel heater at 100% battery power. It took a hour or so to reach the asked +19 inside the car and at the time the cassette was at +2.
In the morning at 07:00 when we woke up outside was still at -18 and inside the car was +19 as set in the control panel. Toilet cassette was at +18, so the cabin heater can easily keep the toilet waste from freezing even it's really cold outside. Battery power was down to 30%. And we could hear the Truma diesel heater work for entire night. We don't have any isolating window covers yet, but most likely will be getting a set of those at later time.
But all in all, a night in -18 celcius degrees went well and 12 hours of heating drained 70% of the battery and we did not get cold inside. =)
Just to let you know if anyone finds this useful.