Storing gasoline for a month, or 6 months will have no measurable effect on its quality or performance. None. It takes years for gas to go "bad". I am speaking from decades of experience with automobiles, classic cars, motorcycles, lawn motors, and snowblowers. Fuel additives beyond what comes from the pump are a waste of money.
What WOULD be helpful would be to make sure you don't leave fuel in a carburetor. It can evaporate and leave a layer of hard-to-remove varnish. Turn of the fuel supply upstream of carb and let the engine run dry.
Formerly: 2005 Airstream Interstate (Sprinter 2500 T1N)
Now!: 2014 Great West Vans Legend SE (Sprinter 3500 NCV3 I4)