I like Stabil but any stability additive will probably solve your formation issues. Your environment can definitely be part of the problem. Gasoline is subject to being attacked by microbes (bacteria); it begins to deteriorate as soon as it leaves the ground at the well, actually, since almost all oil wells are contaminated with the relevant bugs. But like any microbes, heat and humidity can increase it's activity, and can also cause water contamination in fuel storage or the device's tank, which feed the things. All the fuel stabilizers will have fungicides in them for this very reason.
Alcohol is a fungicide, your use of Alcohol free fuel might be contributing to the problem. As for what to use, the only thing I would say, as it seems important to you, is Sea-Foam contains alcohol.
I too agree that you should be mixing your own fuel. Premixed anything is generally the most expensive option in my experience, and you can be pretty much assured they are using the cheapest products they can find as their base ingredients. Maybe super-cheap isn't so bad, but in that case shouldn't you be choosing exactly which bargain brand stuff to use instead of a company whose mandate is to profit from their choices?
You could probably get "pure fuel" at the airport or a local track.
