Somebody just don't try much. You want to run over water, make a flying boat.
1 cubic cm of air space can float just next to 1 gram of copter. 1 lb is 454 grams, half a liter.
The fans don't touch (room between) and the bottom has no propwash. Floats can go outboard of the props.
Maybe the fan ducts could also be floats.