Rincon, I think you solved the mystery! That website (published by a water softener company) concludes:
“Soft water that does not contain enough mineral content to be conductive will not allow the proper electrical reaction between the anode and the steel tank (cathode). If there is little or no electrical reaction between the anode and steel tank, then the tank will not be protected. If the tank is not protected, it will rust sooner than designed.”
And since we always fill with mountain water (which is very soft -- it is snow-melt -- does not rinse off soap well but does not dry the skin, either) -- it could be that there is no conductivity inside my tank, so the anode is just sitting there, doing nothing, and that is why it does not corrode!
NOW what to do? I could bring hard water from home, although I do not like to tow with full tanks. I could put in a magnesium anode -- maybe that will give me better protection than the aluminum anode? Or maybe I just leave it all alone and hope for the best. I suppose I could drain the hot water tank after every trip and leave the anode out -- that is a minor hassle, plus insects could build a home inside the empty tank, coming in through the anode socket.
Not sure what to do, but the collective "we" are onto something, I think!
This business about the anode not corroding sort of reminds me of the Sherlock Holmes story about the dog that did not bark -- sometimes the absence of an expected event is itself significant. Too bad I am not Sherlock Holmes, though.
