I think your floats at 11.5 inches may be a bit on the short side. I'm not sure of the fuselage length of the SS cub but a gereral rule of thumb is for the floats to be 3/4 the length of the fuselage and this is for larger planes. For a 1/2A size I would make them at least that length or a bit more. The only successful 1/2 A seaplanes I have seen are the flying boat type like the Aqua Star.
Good luck