I have the same rear fog and reverse lamps and have not found they leak or work loose - plenty of bumpy roads here. Perhaps they are better sealed against water than the front indicators for example, which may be why they were chosen for that location.
I did work out that they could probably be replaced using the rubber mounts for front indicators (the angle is the same but inverted), plus Lucas fittings as per the upper rear lights, but haven't done so.
