Burl-
This thread had been going since Feb 2002 when Daniel C. started it. Sometimes it gets slow and sometimes it hops, but always people only answer when they have a good answer or have had experience. From the silence I would guess that no one has measured the movement of the upper shelf. Since my B+ bounces at least an inch on our local roads, I would guess that the upper shelf is moving that much also. The real issue is the relative movement of the shelf versus the frame of the motor home.
So I apologize for a poor answer since that is the limit of what I know on the subject. Any one else help?