The part about condensation forming in any above-ground tanks that have low fuel levels is a very important issue.
It becomes even more important when the tanks cycle through wide temperature variations over 24 hrs, and there is high humidity present.
Even the lowliest, but well-trained operator of any ground-based item of powered machinery, knows about refuelling at the end of the working day to ensure no room for condensation to form overnight in the tank of the parked machine - which will happen if left with low fuel level. Emptying any above-ground tank on a daily basis, and leaving it empty overnight on a repeated basis, will lead to a sizeable volume of water in the tank, if not drained very regularly.
Below-ground tanks suffer much less from condensation problems, due to the fairly constant temperature of the soil.