We just bought (out of pocket) the Inogen One G4...the newest and smallest model. So pleased with it! Medicare will only cover the G3 (when we checked). Look at Inogen's website and compare the specs for both to be sure which one will suffice...different size, weight, flow settings, etc.
Comes with both regular electric plug and 12v plug for recharging the battery. Just push a button to turn on, instead of always changing a regulator from one bottle to the next.
Also, we did not know until recently that there exists a 4-ft canula. Have used 7-ft for years. Who needs 7 feet from the bottle (or Inogen) to nose? So the 4-ft canula helps to not be constantly tucking in or flailing around with extra tubing.
Of course, while inside RV, just use a regular big concentrator with 25 ft hose.
We've had to change our RVing lifestyle to stay at more campgrounds with electric hookup. Yes, we long for the boondocking, forest road exploring kinds of days. Fortunately, we had many good years and wonderful memories doing that.