Propane tank

Anyone got advice on how long a tank of propane lasts?  We boondock a lot so use the fridge on propane and the water heater.  

Like anything else in this business, it depends. The fridge sips Propane so a tank will last forever. Maybe several seasons. The HW heater uses more, but depends on how much showering and dishwashing you do. Usually if you're taking lots of showers you are in a campground with hookups and using the electric HW heater. The big demand on Propane is the furnace. If used heavily it can deplete a 20# tank in less than a week. A good solution to Propane is to have dual tanks with an automatic switchover regulator. If you stay with one tank there are methods of determining Propane level including weight, temperature, and ultrasonics, but they do not include the gauges you screw onto the tank top. Buyer beware. 

As Charlie stated above, "It depends" and he is correct.  We can normally get about 9 months out of 1 tank and we boondock a lot.  The largest culprit of course is the furnace and when we were in the RMNP last September night time temps were normally in the upper 30's to mid 40's so the furnace would go on quite a bit.  During the day we would be hiking so the furnace would be turned off.  If I were to add up all the nights we use the furnace it would probably be 3 weeks worth on a tank + the hot water + the fridge.