I travel extensively and always have lenses mounted ready to go, never yet had a mount problem, maybe I've just been lucky.
But I guess if we're talking transit shock of level to affect mounts, I'm guessing that maybe the rest of the camera internals would also be floating about loose within the camera bag. If it all does goes pear shaped, I pay enough to the insurers to cover my equipment, they can stump up for the repairs or replacements.
The real question for me is, why would you have unmounted bodies subject to inclement conditions?