I did not ground the shielding, nor the GPS ground plane, probably should, but I just have not tried it. My frame is carbon fiber too. You can see my setup in this video: http://www.youtube.com/watch?v=7hA2orjUdCE
I have not noticed any problems with the PWM signal from the RX. My RX is a UHF system (EzUHF). Most of the time I do not use the RX and fly with a joystick through Mission Planner ( that means the control link is via MAVLink and 4G.)
Since the video I have been flying it quite a lot,and over longer distances (several km). It has been very reliable, I always fly by GPS (loiter or mission) and it has been 100% so far. I notice some loss in GPS quality when I turn the camera on. HDOP usually go from around 1 to 1.2, but that is still plenty of GPS signal to fly.