At my former division, we built 4 season coaches for a rental outfit. I personally spent 4 days/nights with that as my base camp for a ski trip in Alberta. One of the first things they had us do was drop the tank heaters. They're just so inefficient, most of the time people were just draining the batteries down causing all sorts of other havoc.
At night, we turned the T-stat down to about 63 degrees and bundled up, to conserve LP and not have the fan running all the time (was not necessary however as we never had battery issues and we still had over half a tank of LP after 4 days). That left enough of the furnace running to take the edge off the utility bay while we were asleep. During the day, the outside temp was 17 degrees and we never had a single issue. We ran everything, took showers, cooked, washed dishes, etc. Now we did build that unit specific for ski season....but the same principles apply to the fan forced system that we're running on the 5 series. The only difference being, we don't add extra insulation to those bays...but cold weather camping and winter camping are two different things.
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