My new van might change things, though. It's probably triple the interior volume, and much less of the side wall area will be insulated with storage stuff. The fridge + body heat might not do as much to keep it warm, and I might end up running a heater sometimes.
I will have a couch, in addition to the bed. It occurs to me now that I should put an electric mattress pad on the couch, like I have on the bed! That plus a heating pad on my lap does a lot to heat the person, rather than the space. The cats, of course, get their own heating pads :-)
I do think I could drive a lot more than I do and still use less energy than I use heating my stick house up north.
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Let's see...
Wikipedia says a gallon of gas is 33.41 kwatts.
To make the math easy, I will assume 10 miles per gallon on my rig and 4000 watts (4 kilowatts) of heat per hour in my house, 5 hours per day. (I figure 5 hours because the heater cycles on and off, and I switch it off at night.)
So, to heat my house for a day is 20kw, or about 6 miles of driving.
Over 6 months, that is 3600kw, or 1080 miles. Wow, driving is a lot worse than I thought!
(edited for more realistic heater usage)