I've always hear of this concept, however, never really understood the science behind it. I never had a problem with it either. What I do know is, in order for water to condense from the air it most reach it's dewpoint temperature. The dewpoint is always less than the ambiant air temperature, even if the relative humidity is 99.9%.
So knowing that, the fuel tank wall would have to drop below the ambiant air temperature down to the dewpoint level. How would this happen?
Spoiled One should know. He's a science type guy.