You can put double the quantity of Stabil in your gas if the boat might be sitting longer than just a few months. Run the motor with the treated gas to get it through the fuel system.
Fogging is best. You spray the can of fogging mist (oil and additives) into the carb of the idling motor until it dies, then you're done with that part.
If you don't want to start up the motor you can also pull the plugs and drip a capful of oil into each cylinder. You want some protective oil coating the rings so they don't start to stick to and score the cylinder walls.
Take a look at the manual for your motor. There are various spots you want to put a couple of drops of oil (linkages, etc.) also.
