Hi Solo, as Mankster and Sub have said, I use a Mtroniks mixer with a Robbe handset. I was initially going to use just one speed control but Mankster said the turning circle was too large, so I mixed mine. For the piston tanks I am using a 3 way switch, with a neutral point in the middle. I did consider a slider but since the tanks are either on or off on mine and not proportional it wasnt worth it.
As they said, I turn the rudder left the starboard motor activates and vice versa. Seems to work pretty well.
Paul