The biggest thing to worry about in regard to ethanol (or any other type of alcohol, for that matter) is carburetor needle jet corrosion and disintegration. Alcohols attract and suspend water. While this may help an engine run more smoothly if there’s water in the gas, over time as the engine sits unused (>50% of time, I presume) the water (in gas) soaking the jets will corrode them, making the fuel mixture rich. Not only will the engine use more gas, but worse, running rich will deposit excessive soot in the cylinder and in the oil. Soot is an abrasive that will cause premature wear throughout the engine. Also, soot on the spark plug weakens the spark, aggravating the problem.
A simple solution, pending the next carburetor rebuild/replacement, or mower replacement, as previous posters stated, is to use fuel treated with a stabilizer/rust inhibitor.
As for rubber parts, I’ve discovered the perfect rubber preservative, if the rubber isn’t too far gone- PB, from B’laster, of Ohio. It’s marketed as a de-sieze penetrator, but a blurb on the side of the can about fixing toilet flapper valves tipped me off about what that stuff is REALLY good for.