Gasoline can generally be relied upon for about a month these days, if it's stored in a tight container. With stabilizer use, that can be extended to maybe a year, though anything over about 6 months can be a gamble.
THe problem is actually not exclusively the ethanol. Ethanol has indeed further reduced gasoline's stability, as it attracts moisture from the air, until there's enough water in there to cause the ethanol to separate out. Ethanol fuel treatments aim to prevent this.
The real problem is that the world is no longer rich in light sweet crude. Crude produced today is generally made of much heavier molecules, closer to tar than gasoline. Those long molecules need to be broken into smaller ones to be burned in our engines. This breaking is called "Cracking", and today's hydrocracked and catalytic cracked fuels are inherently chemically unstable. They degrade quickly regardless of atmospheric exposure.
Fuel stabilizers aim to prevent this. Add stabilizer to each gerry can you buy, and you'll not have fuel problems. Restrict your purchases to only 1 or 2 months worth of gas at a time. Don't store gas for next season - add it to your vehicle's tank before it goes off.
Modern gasolines are a real headache for small engine maintainers.