Prep
I have been using the WM bottom paint ($$) for inflatables for many years (9+). At the end of each season, I gently power wash the bottom when it is still fresh from the water. I then scrub the bottom with a stiff brush and some of the acidic hull wash/cleaner available at WM. I use a Scotchbrite pad on some of the tough spots. Next season, I put on a thin coat of the bottom paint and let it dry. No barnacles, no flaking paint.