That's the same series GPS that I have, but I mounted mine in an Aquabox to isolate it from vibrations (killed my old TomTom) and make it weatherproof.
How are you powering it? I powered my TomTom from a
Powerlet socket inside the front fairing, but for the Garmin I fitted a
3BRpowersport USB port to the handlebars just below the mount.