I may be wrong, but I actually have very little gas in the tank when I stop driving. I like fresh gas in the spring and don't drive enough to finish off several tanks, or even one, of gas in summer. In my case, the storage area is 68 degrees, 50-55% humidity and doesn't vary all winter. So, i think condensation in the tank is a non-issue, but I could be wrong. I do understand in varying humidity and temperature environments that condensation in an empty tank could be an issue.
I actually disagree with washing a car just before storing. Water sitting in all sorts of places unseen, not good, in my opinion. In fact, I don't wash my cars at all, just detailer. The Pagoda is going on 11 years without a wash. I do wash the wheels and tires. Of course, the car never sees circumstances that a detailer can't handle.