Once I heard when I was young that if you keep your tank low you increase the amount of condensation in the fuel tank. It makes sense, since condensation is moisture coming out of the air and if there is more air then there is more moisture assuming that condensation occurs. I therefore try to keep cars filled more rather than less, particularly if I am not driving often.
If you have a car but you bike to work, then you car may stand idle a lot and then in the day all that air in your empty tank heats up and expands. Then in the evening as you peddle home, the air cools and drops its moisture on the walls of the tank while sucking in more cool air to make up for its reduction in volume as it cools. Then the whole process repeats itself. Over and over and over.
If the tank is full of gas, then the amount of air bringing in moisture is less, so less moisture. One can't argue with this logic and still be logical, but one can argue that the amount is meaningless.
Since I heard it whispered when I was in the womb, it is too entangled in my noggin's thinking bits for me to shake out.
p.s. Do you think this is more or less true in the desert?