I never worried about my propane tanks, how full or how empty they were on any of my travel trailers. And now that I have a 5er, I'm still doing the same thing. Simple technique:
Keep one tank shut off completely and turn the other one on. Use it. When the gas runs out, close it and open the other one. Then immediately go and get the empty tank refilled. 60 years of camping experience with my parents as a kid, family, friends, and my own campers, and never ran out of propane doing it this way.
I have learned to anticipate my propane usage. If I begin to question how full the running tank is, for example getting ready for a 2 week trip and want to make sure I've got sufficient propane, I simply loosen the tank and lift it up a little. The weight by simply lifting tells me how full it is.
And yes, you take the tank off the RV and take it to a propane refill station. You can drive your camper to the refill station, but you'll still need to take it off the camper yourself.