I appreciate all the replies and ideas.

I thought that maybe there was some kind of water proof boot that would mount on the back of the float(s) sealing a push rod exiting the back of the float.

I'm building a KMP Beaver so I'd like to keep it some what scale. But, As I never seen up close how a full scale is rigged up, I'm assuming I would have to run 8 cables up to the plane for a dual water rudder setup.

2 for each rudder - pull / pull and 2 for retracting water rudders pull/ pull. Please correct me if I'm wrong. ( this is why I asked my original question)

I found a good web site on Beavers pics but have yet to find a close up on the cable rigging for the plane.

I'd like to keep it simple but definitely no nyrod looping down the outside.