We use the Fly sky FST6  model transmitter 

Fly Sky      set up 

Rudder Servo

We use this digital rudder servo that we find turns the rudder very fast  Hiteck HS-5646

Standard Digital HS-5485HB also works well with the D4

D4 Rudder Servo Installation

Sail Winch 

290 EF has been most effective winch for the D4

D4 Winch Installation video

Waterproofing electronics