Is it necessary to add fuel treatment to my gas
tank with the occasional fill up?
I would recommend something like Techron twice a year.
I would recommend Techron too. It provides lots of money for Exxon retirement packages..... Today's gasolines have the best additives in history, and as long as you don't by gasoline form the Dollar Store pumps, straight pump-gas is really all you'll ever need.
Usually the gasoline have enough additives in it without add more to it. If You fill up occasionally the bigger problem in Your gas tank is condensation . To eliminate that is ,to keep Your tank full all the time or add some water eliminator additives like " Heet" or other contain alcohol