To answer those who have inquired:

I had a Yakima rack with Double Cross Towers that held round cross
bars on top of my Dodge Grand Caravan with existing factory rack.
Worked great. Took it off and was able to use those towers on the side
rail style roof rack (no cross pieces) on my new Pontiac Vibe 2008.
Despite the different size and shape of the side rails on the Vibe,
the Double Cross Towers worked fine.

Mel Packer