I haven't flown it with the floats. There is not enough clearance for the seven inch prop supplied in the kit. You might try a three bladed, six inch prop. I have another one on the bench that I intending to try flying with floats.
I don't think it will be possible to ROW with rubber power since the three coats of clear dope required to waterproof the floats and the plane it would add quite a bit of weight. (For those, like me, who use Krylon fixative on the tissue, Krylon is water resistant, NOT waterproof.) Of course, there is always one of you that will just have to prove it can be done.