I would concur with Neducati. I have never had a problem with the key mounted in this way on my Scram and I do ride in the rain!
Well, I did have mine freeze solid... But the lock on my Givi case was frozen too. Had to pour hot water on it to unfreeze it(temps were in the 20's), and then sprayed some graphite lube in it after it warmed up and that seemed to solve the issue, but it wasn't quite as wet the next time it got that cold.
The relocator makes it a LOT easier to turn off though... Before I would have to shift into neutral so I could reach down with my left hand. You would think they would put the switch on the right side to begin with, or even on top where it SHOULD be anyway!
It seemed like a tight fit - I had to file away some material from the bracket to get the switch in. They didn't change the switch at all, did they? Either way, it works great now.
Becsta - the bracket screws into the holes on the handlebar clamp, the only thing that would be in the way would be the Triumph accessory tach for the Scrambler which normally mounts there. Just unscrew the cover and see if the extra mounting holes are still there, I imagine they are.