I mix avgas with ethanol 91 and find that running avgas mixed with 91mogas it keeps for long term in my snowmobiles. I run it in a boosted snowmobile and it sits all summer and never have a problem with octane the following year. Doesn’t seem to take much avgas to help stabilize the mogas.
I am currently running 91 ethanol in my plane.😬 If I where not flying often then I will put a tank of avgas in it.