You can leave E85 sitting. The fuel system is ventless which means fuel can be sitting for months and not degrade significantly. Infact, I don't use fuel stabilizers at all on new stuff. I leave the tank low and refill as soon as I get back. It's only necessary in my humble opinion to use a fuel stabilizer on gas cans because they can and do leak. I never leave fuel where it can fully vent to atmosphere. Gasoline can break down over time and Ethanol can evaporate and absorb moisture. Moisture can cause phase separation in Ethanol blended fuels. You can actually test it by putting fuel in a jar.
I left my car to family last time and came back to a dead battery. It ran fine for months but after four months of sitting they just didn't drive it enough. I didn't have a safe spot to leave a battery tender with the shed being used as a fuel depot.
Oh well. I recharged the battery and then I drove it for a solid hour to get fuel and warm up the tires. That was 6 months ago.
But you can do your own research. My grandfather was a mechanic but that doesn't make him an expert on fuel storage. And don't get him started on the new stuff.
