I've been full-timing for about 15 years now, first aboard my 2005 Casita 16' Spirit Deluxe, bought new in Sept '04, and now aboard my 2014 16' Freedom Deluxe, bought new in Oct '13.
I'm from the Carolina foothills, with maternal blood from Central Georgia, so anything below about 75°F is sweater weather. To give you an idea, I often run the furnace for a few minutes on a cooler summer evening. One time in Raleigh for a couple of days at 101°F in a sunny spot, I didn't even turn on the air conditioner - just opened the windows
and ran the Fantastic Fan.
On both trailers, the setup was/is the standard 2x20lb tanks with auto-changeover. I've never used that feature, as the tank cover obscures the view of the green/red indicator. I have just made it a practice to have the empty tank filled within 2 days or so after switching over. (One time, about 12 years ago, I ran out of gas about 9 pm during a light
snow, and abruptly realized that I had not filled the other cylinder. I used a cylinder exchange at a local convenience store that night. I kept an eye on my nicer cylinder in the cage that week, and when the swapped one ran out, the store traded me back my original, empty-for-empty.)
Nowadays, I'm mostly on shore power, so I use a $20 ceramic cube heater most of the time, and run the refrigerator on 120V. That leaves heating a tank of water once per day and heating 1-2 kettles for coffee for the propane. At that rate, I'm only refilling a cylinder every couple of months.
I used to spend 3-4 days per week on the road, off-grid. 15/20 watts of solar
(1st/2nd Casita) provided ample energy for lighting
, water pump, exhaust fans, and furnace fan. The propane load included running the refrigerator 24/7, running the furnace from around 9pm-9am, heating a tank of water per day, and the aforementioned coffee making, with limited cooking. Under these conditions, one tank will last me around 10 days.
In warmer weather, taking the furnace out of the equation, the interval is more like 3-4 weeks, off-grid.
As stated above, your results may vary!