Seafoam might fix your problem here. Props (pun intended!) to the person that said that. But that's only if you have water in your gas.
Yes, Stabil works and works quite well. I have used both the "Marine" and "Regular" versions of the product and both do what they claim to. They will keep gasoline that's properly stored (out of the air) good for 1 year, perhaps as much as 18 months. I am not sure what the difference is between the regular and marine versions, but as the bottle says "overuse will not harm the engine" and it doesn't seem to.
Personally I keep a number of DOT certified METAL 5gal jerrycans around, some for the cars/trucks some for the boat some for other things like chainsaws. I add the recommended amount of Stabil, add 1/2 more ounce and then fill the can. If the time expires on them, I rotate the gas after 1 year. If you plan on storing gas that long, put a date tag on it.
If you're concerned about your on-board fuel tank. Add the Stabil before gassing up near the end of the season. If you screw up, simply read the label, add the needed amount when you trailer and let the bumps in the road do the work of mixing it in.
So yes, it works and works well.
Stabil does NOT keep water out of your gas, nor will it help with it.
Gas MUST be stored in a SEALED container. And NO a cheap plastic jerrycan doesn't fit the bill, nor does a plastic outboard motor gas tank. Proper storage is with a metal, DOT certified can with a large rubber O-ring seal and a metal lid.
Stabil only stabilizes unstable aromatic hydrocarbons within the gasoline that will cause the gas to go bad within a couple of months. It will not affect nor will it prevent "wet" gas AT ALL. For that you need a different product like DryGas (seafoam) that actually removes the water from the gasoline. DryGas simply adds ethanol to your gas (increases what's already in there from the pump thanks to the feds). Ethanol is a dehydrating agent, but in solution with something like gasoline it does two things: drives off water from the solution and prevents water from freezing in the solution.
For water in your gas, if that's your concern buy a yellow bottle of "DryGas". I used to use it in the car all the time when I lived in places where frozen water in your tank might sideline your vehicle for a few months. For gasoline storage however, Stabil is a great buy.
A final note: if your gas is simply old and was not treated with Stabil or a similar product, it's probably shot. Still flammable though. Great for starting camp fires really fast (and fun!), but no longer useful for running an engine. Untreated gas, stored away from the atmosphere has a maximum effective lifetime of about 3 months at best. Usually it's more like 2 months. If exposed to air, that lifetime decreases.
Best of luck!