A picture may speak louder than words...December 1, 2007, 40th Street Boat Launch in Bellevue, about to head to Andrews Bay in Lake Washington for the weekend...
TubeRider, the short answer is that leaving a lot of air inside the tanks allows moisture to precipitate out, i.e., to "rain" inside your fuel tanks. When you go to head out next Spring, it will take a little while for that water to get into your filter and engine and then you may wish you'd filled up.
Recently some have posted that it is no longer necessary to maintain full tanks, but I do not remember the exact reason that is OK now, but not a year or two ago. I am thinking it depends upon your local weather and use patterns.
At any rate, I'd advise you put HEET and StaBil in your tanks over the winter to absorb any water and prevent fuel aging.
