|to absorb the moisture when the ethanol does it fine.
What happens is the moisture in the air condenses on the cold surface of the tank. Then it drips or runs down the tank into the ethanol and mixes with the ethanol. E85 can take a lot of this moisture from the air before there is a phase separation problem. This water-ethanol mixture burns in your engine. The moisture in the E85 works like water injection to improve your octane.
If your tank is filled with gasoline, the water drips or runs down the walls of the tank and cannot mix with gasoline. Then you need a stabilizer to absorb the water and make it mix with the gasoline. I prefer to use ethanol.
Filling up your tank means there is less air and less moisture to condense. My concern is that rust tries to form mainly at the interface of the fuel and air. If every winter you fill your tank up to the same level, every winter the rust is trying to eat away at the same place. For this reason, I don't really concern myself with the fuel level when the car is parked for the winter. I'd probably be best to fill it to somewhere in the top 1/3 of the tank, thus minimize the water vapor in the tank without filling to the same spot every winter. Either way, the ethanol easily mixes with the water.