I'll do one better. I have the same Garmin and I use a Touratech mount. cycoactive.com lists the mounts on their website. They aren't cheap but the one I have locks the Garmin in the mount with a cylinder lock, has a dock for the xm antenna built in and a power cord dock built in as well. They have full suspension. Really a quality mount and you get what you pay for.
www.cycoactive.com