One tower slipped backwards up to maybe an inch. Another friend of mine has had that same problem with the Q-Towers on her Civic (I believe that's the make of her car) and she's scratched/pitted her roof and door "gutter" quite a bit from the Yakima Q-clip---and I've heard that the person I sold my Q-Tower rack to wound up breaking the tension/clips (probably trying to get things to stay fixed). That all said, I've had one set of Q-Towers on a Subaru of mine that have been rock solid for about 9 years (finally had to replace the towers as they were rusting out in some key areas).

I like your solution of mounting a solid bar between the cross-bars. Seems like a good way to keep things more solid.

Again, I'm very happy with the way I went with permanent track mounting. I tend to keep my cars forever, so am not at all worried about resale problems down the road.