The screws and mounting plate supplied with the ZR2000 remote do not open sufficiently wide to fit on the large diameter of the 503 pan handle. I could find longer screws. Any other suggestions for a secure mounting that is easy to assemble on location?

Best,
Christopher

That is annoying, isn't it? I can live with how "plastic" the Canon ZR series controllers are, but that limited handle diameter thing is rather poor. Longer screws are your best option. A trip to your local hardware store... be sure to take the current screws with you, plus the controller, to make sure the threads match up.