That'll work, and it is light.
A more scale way would be to take the cables along the bottom of the fuselage, to the top of the landing gear strut. Scale planes have a pulley here, but a dubro 2-56 eyebolt works fine. then route the cables down to another pulley/eyebolt at the bottom of the strut, and back to your water rudder. if you are using 2 water rudders, you can set up 2 linkages. You may find that the pullpull you have across for the second water rudder becomes overstressed if you land harder than you meant to.

I found that I stopped damaging the horms on my Ernst Water rudder after I installed little bronze springs at the ends of the cables. If the water rudder takes a shot, the springs let it flex, then snap back, without damage.