I'm trying to install a Mopar roof rack on a 2002 Chrysler Voyager SWB.

My problem is with the expansion nuts, I cannot get them to expand.
I used the method illustrated in the installation instructions: use a bolt, nut and washer to expand the expansion nuts. My problem is that the expansion nuts turn in the hole in the roof when I tighten the nut, so the expansion nut does not compress.
What is the trick behind getting the nut to expand?

 

I applied some lateral thinking and came up with a solution.
I cut the head off a 7mm bolt, filed away some thread so I had a smooth shaft to fit in my pop riveter, screwed the nuts onto the remaining thread and pop riveted them in.