Condensation in fuel tanks is one of the most exaggerated machinery phenomenons there is, and the introduction of ethanol into fuels has only fueled the fire even more. I belong to a boating forum as well, and the number of products that have been posted there to deal with fuel tank condensation, and ethanol "sucking moisture out of the air" is almost unbelievable.
Often, the links to the products being marketed towards the owners that are the most fearful of dreaded fuel tank condensation show "proof" like laboratory beakers with water in them that allegedly "condensed" in the fuel tank. What they don't show however, is any real math that supports their allegations.
A fuel tank has a definite volume of available space. The surrounding atmosphere can only hold a given amount of moisture. So given the amount of moisture they say has "condensed" in the tanks over a given amount of time, they need to explain how it occurred. They seem to be contending that, (especially in the ethanol examples which they know folks already see as scary), the fuel tank condensed all or most of the available moisture out of the "air space" in the tank. Then, the tank expelled that "spent" volume of air, and sucked in a fresh moisture-laden volume of air, condensed all or most of the available moisture out of it, expelled it....and the aforementioned process repeated itself until the shocking volume we see in the laboratory beaker has collected.
The numbers simply don't add up. I don't know why, but showing the water in a laboratory beaker being held by a paid spokesperson that a rented lab coat happened to fit is enough to convince lots of folks that there's some science going on....