If you are building the rudder assembly from the Kit, be aware that the spacers for the rudder housing and the rudder itself are the same thickness of plywood. If you assemble them, according to the manual, the rudder will be too thick to fit in the rudder housing.
Pre-check the fit before you add the fiberglass, epoxy and paint to both pieces.
I am in the process today of using a router to plane down the rudder by 3/16+ to fit in the housing.