Tested my 2011-8528BHSS three years ago. Got down to 15f in Chicago. Two ceramic heaters, ended up freezing the water pump (thawed out ok). Partly my fault, didn't use the furnace strong enough that night. Had tank heaters on and fresh tank was full as we anticipated the drop in temp. Used up a 30lb tank of propane every 3-4 days. The local propane company offered free of charge to install 100lb-ers. We had to order new windows forward as the glue dried and they were leaking water excessively (when it was warmer). Don't know for sure how much colder we could take her but she came through strong and proud to have her.
Don & Dona W/yorkies Gizmo, Master Chief, & Tali
2011 Flagstaff 8528 BHSS 2015 Ford 6.7 XLT
2010 Full Timers & Still Going