Since there are no rubber diaphragms in the carb, I wouldn't be overly concerned with alcohol related problems.
I've spent a lot of time analyzing this issue when I had a vintage motorcycle repair and restoration shop full time. From my observations the only verifiable problems with gasohol (E10) came about when the fuel was allowed to sit over 10 weeks. At that point. There was some separation in the fuel that was detrimental to rubber parts of the fuel system that were old to begin with. Other than that, over a period of many years and thousands of engines, I have not seen one case of E10 related carb problems.
If draining the fuel from the carbs and gas tank is not possible (and why not ?) when the vehicle will be sitting for 3 months or longer, a can of Stabil will do wonders to keep the gas viable.
These photos are not E10 related, the owner of this Yamaha XS1100 used only "pure" gasoline. He just let it sit way too long. But they are too juicy not to pass along. As you can see, gasoline does not always "just evaporate" without leaving something behind.
Enjoy.
Z.