I have outboard motors as well as chain saws, wackers, etc. All are in the shed in a non-climate controlled atmosphere, thus moisture is always a problem.
I only use E-10 for that specific reason. I wouldn't think of buying pre-mix because you never know if the guy mixed it right. I DO know my mixture is perfect. And if any moisture ever gets to be a problem I know the E-10 will burn it no problem.
Just today we took our old classic car out for a Sunday spin. Maybe a 100 miles a year, so the gas tank gets filled only about every 2-3 years. ran like a top. On the way home I filled her up with E-10 ans Sta-Bil. Good for another 3 years.