The Touratech holders are rock solid and takes many gps models including the zumo, it comes in aluminum and black versions, with or without lock. They are rubber mounted to reduce vibration:
Here it shows a GPS mounted, unfortunately they did not have a picture of your zumo model on the site.
There are two mounts, Touratech's non adjustable version and KTM's adjustable version:
I have KTM's version with a rubber mounted holder for my 276 Garmin GPS, its the unlockable version as it makes the GPS sit a bit lower, but still makes all readouts visible even tough I'm medium-tall.
Installation is super easy. There are picture as well as text instructions following the product showing how to do it. You remove the tanks/side panels, as well as the front wind screen (all you need to do is remember what bolts you took out of where), you can see all bolts you need to remove on the outside of the bike. When they are off, you mount the lower part to the front "sub-frame" in existing holes, then you drill holes through the top panel (can't remember the size) and mount the top part through. Attatch everything again... Simple and quick. I used perhaps 45 minutes (and I'm no mechanic.)