I'm not an electrician, but this is my opinion.
Get rid of that ground wire to your switch. When the switch is in the off position, you're connecting neutral to ground through the motor, probably doesn't look good to a GFCI.
By the way, if you are using ground anywhere in your system as a return path, it is wrong. That's what neutral is for. Ground should be connected to your metal faceplate and frame, if they are conductive.
Another thing... Find an electrician and give them some homebrew to look over your wiring. You're working in a wet environment; a mistake can kill you.