Nope they haven't moved...
They were a couple of mm oversized so they took some getting in there... They aren't coming out... Besides they are bolted and the female side of the mount is less than 10mm from either end - they couldn't move any more than 8-10mm out of place anyways.
If you were still worried you could just cut them larger - and hang some over the edges like the ones rob posted above...
And if they start to squeak then spray them with lanolin - should do this anyways to stop them becoming brittle..
