AV gas has enough preservative in it for 5 years; pump gas 6 months. I dont worry about the ethanol doing damage; it is when it absorbs water and that does the damage. Fast temperature changes will make the water condense into the fuel the it is easily absorbed. AV gas tho is blended with some things, that while it is used constantly, everything is just fine, but let a diaphragm dry up after use and it accelerates the dry rot.