Iv'e had good luck using stabil for about 20 years or so and my storage time is usually about 6 months.
You could give PRI fuel stabilizer a try, link below or you might just completely drain the fuel out of the small equipment.
I have not personally tried the PRI, but I would if I had a need for longer storage times. https://www.amazon.com/PRI-Fuel-Stabiliz...ywords=pri+fuel
When you add the stabil, do you allow for a good mix with the fuel and run the small engines so that the additive is well distributed through out the fuel line, carburetor and etc?