I fulltime and try to always subscribe to the KISS principle as that usually works best. I don't use gauges or the hot water method. I have a fiver and 2 tanks. I open one tank and keep the other one closed. When tank #1 runs out, I manually switch over to tank #2 and take tank #1 to get refilled. When tank #2 goes empty, I just switch back (manually) to tank #1 and take tank #2 to be refilled. Repeat as necessary.
The advantages are that you don't have to remember to check anything and don't need any (inaccurate) gauges. The disadvantage is you may run a bottle out of gas at an inopportune moment such as the middle of the night when running the furnace or when driving down the road running the fridge on propane (happened to me last summer).
The only exception is that I always leave my winter quarters with 2 full tanks.
I would not want an auto changeover set up. You might not notice you have switched from #1 to #2 until it's too late to get #1 refilled easily. Or worse yet, you run them both empty.
Tim.