For cold camping conditions, we do the following with our E350 cab area. I can't say to what rating it's good for, but it works for our particular rig to a low of around 28 degrees F.
- set the climate control in the dash to "recirculate"
- cover windshield and door glass with pop-open sunshades, but custom-fit insulated shades would be much better
- drape and tuck a comforter over and around the two front seats, creating a sealed and insulated barrier to trap the cold air in the cab
- when 110v is available, we place a small cube heater on the floor near the cab and blow the warm air rearward towards the house interior.
- not related to the cab, but we also draw the shades in the house
Our interior is small, has no slide-outs, has a lower ceiling, has thermal pane insulated glass, and a well sealed entry door. General air leakage and radiated cold is less with the quality build of our rig which further helps with interior comfort. With everything considered, the main house furnace operates much more efficiently. At bedtime we close the bedroom curtain to trap bedroom heat. The thermostat inside the enclosed area then works off that trapped heat with us inside it, further reduces furnace cycling which reduces our concern for battery and propane usage.
CLICK HERE to see our rig's interior and curtain. The curtain is thin but helps a lot.
