Where you are camping, when you are camping and the weather are the variables which control your propane usage.
On average, I find that if I do not use the furnace - as full-timers we can run the stove for four to five months before we use up one 30lb/7gal cylinder of propane.
We tend to run the hot water heater on propane if we are camping in the summer on 30 amp power and using the A/C. We only turn it one when we need it. That increases our usage to about one cylinder of propane every six weeks.
When using the furnace and temps are below freezing in the teens at night, I get less than two weeks from one 30lb/7gal cylinder. That includes running the 1,500W fireplace electric heater that came with the TT, and a supplemental 1,200W heater the DW wants in the bedroom.
When low temps are near 50 degrees - we use about one clyinder worth of propane every four to five weeks.
This year I've bought 93.85 gallons of propane at an average price of $2.77 per gallon. That's almost 14 cylinders of propane purchased.
We started the year near San Diego, spent late Jan, Feb and the first half of March near Dallas. We headed back west and arrived in California in early April - and are now on the coast of Washington where the low last night was 49.
Last year, I bought less than 30 gallons (4 cylinders) of propane totale. We were in Texas all year until mid-October when we went to Colorado/ Utah/ Nevada/ California. Most of the propane was used in the San Diego area.
This year, we have run the AC at total of 9 days. And five of those were in Arizona in March where the temps were in the high 90s.
Last year, we ran the AC over 270 days, with 119 days over 90, 26 days over 100 and 14 nights where the low temp was 80 or above.