you need these metal rails... known as the c channels--- to be able to use the cross bars.
(the c channels were standard on ALL traverse in 2009 whether you ordered the cross bars or not. Early build 2010's had them standard. then mid year or so- they were removed from all models).
If you wanted cross bars, you ordered a kit. there was 2 kits available at the time.
kit 1- was only the cross bars. (fit 2009 and the early 2010s)
kit 2- had the cross bars AND the c-channels- which was suitable for all Traverse without the factory c channels.
here are some aftermarker c-channels
For 2009-2017 Chevrolet Traverse Removable Roof Rack Side Rail Cross Bar Black 19244264. 2009 2010 2011 2012 2013 2014 2015 2016 2017 Chevrolet Traverse. Fit For Chevrolet&GMC. 1 Pair roof rack side rail.
www.ebay.com