It isn't quite as cold here Jim328RLTS as where you are (+9 F), but plenty cold just the same. In prior years since I started full time the coldest I have experienced was +13 F. I too have a very comfortable interior temp. My furnace has no problems keeping the temp at 72-73 and the only place I notice any real "cool" is the floor in the dinette slide and it isn't that bad. The double pane windows work great and I have never seen condensation in the 5'er anywhere.
2006 GMC 2500HD CCSB 4x4 Duramax/Allison, Titan 52 gallon fuel tank, Prodigy Controller, B&W Companion Hitch
2010 Jayco Designer 35RLTS, Cummins/Onan RV QG 5500 EVAP, Progressive Industries EMS-PT50C, TST Systems 507 TPMS, RV Flex Armor Roof