I have a Open Range 399 BHS. It does well in moderate cold down to 20ºF or so.
The current 3X models have even more insulation than my 2012.
Nevertheless I don't think they are built for extreme cold.
If you want to RV/survive in extreme cold there are better brands. Artic Fox , Excel, DRV are a few.
19'Duramax w/hips, 2022 Alliance Paradigm 390MP >BD3,r,22" Blackstone
r,RV760 w/BC20,Glow Steps, Enduraplas25,Pedego
BakFlip,RVLock,Prog.50A surge ,Hughes autoformer
Porta Bote 8.0 Nissan, Sailun S637