You can get fogging oil in a spray can at most auto parts stores (NAPA etc.). I use a product made by Seafoam which comes in a spray or a pourable form. I pour it in the carb until she stalls at an idle. You can use the spray for this also. Then you know the valves have been coated. After that I pull the plugs and spray some into the cylinders, replace the plugs and roll her over a few times to coat the cylinder walls and rings. When I'm done I drain the gas out of the carbs via the drain plugs on the bottom.
Boats are to be made of wood, otherwise, God would have grown fiberglass trees.