When not going on a "snowbird" run (January to April), that means my motorhome sits from November to May. With my 75 gallon gas tank, I fill it up and add an entire bottle of Sta-Bil and then, with generator running, drive it for about 20 miles. Then it gets parked. Does the STA-Bil work? I have no idea. But I feel better.
Why, you might ask, I ask "does it work?"....well, this past winter, my Harley Davidson was parked from September until 2 weeks ago. 8 months. NO STA-Bil. The motor started on the third hit of the button and ran just fine. In fact, only yesterday did I put "new" gas in it.
However, I will continue to use STA-Bil in the motorhome...so I feel better, and, as it surely can't hurt.