We have winter camped in 2 of our Sunlines over the years. Our 2004 T2499 and our current 2004 T310SR. We have camped down to about 10F at night being OK inside, but it was only after upgrading some areas in the camper. These campers are not really made for a lot of camping below freezing, but there are some upgrades you can do to make them work.
Does your furnace ever shut off in the weather you are in now? Has the furnace worked before and shut off sort of like to is supposed in the recent past, just say the temp at night only made it down to about 40F?
If your furnace is running and heat does come out of the ducts, odds are favorable it may be working the way it is supposed too. One of the issues with below freezing camping is not so much the furnace, but losing the heat we have. Your furnace can't keep up with the loss of heat.
The windows, and roof vent covers are 2 of the biggest losses. We would put foam cushions up in the vents and shower dome to stop the heat from going out and we use shrink wrap window film on the windows. That helps a lot.
We also bring an oil filled heater and or a ceramic portable heater. These are only 1,500 watt heaters. We only need one of them. We also run a separate 12 awg extension cord into the camper to run the heater. If you do not have a heavy gauge extension cord, you use wall outlet by the kitchen sink on your 2006 camper. Sunline calls it the galley outlet. There is not a lot of other things on that circuit, so it will not trip the circuit breaker as fast. BUT, shut the heater off if you microwave. And run the water heater on gas, not electric. Heaters in a camper draw an good amount of power, and you only have so much to start with.
One heads up when camping when it is cold out, heavy condensation will build up in the camper when all sealed up with people living inside. The condensation will create issues over time if not dealt with. We leave one ceiling vent open a good 1", farthest from the bed room to let the moisture out. Yes, I know heat goes out, but you have to vent it. And we also use a dehumidifier. The shrink wrap on the widows helps stop the heavy moisture from forming on the windows, but it still will condense on the window frame as it is metal all the way to the outside.
Here are some of the many posts on winter camping in a Sunny, and things to help with the heat loss.
The window covering and moisture control is talked about in those threads also.
Hope this helps
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499, 2004 T317SR
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC
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