I looked into this - fitting the rails is an involved process, and you either have to use rivnuts (which I'd worry would stress the roof in the wrong way and lead to cracks) or weld the fittings on as per Chrysler (which would presumably involve painting the roof once done). The Thule ones clamp into the door apertures.
Must admit that for all the discouraging noises I saw about the factory rails, if I had the money and found someone competent to do it to the right factory standard, I'd have them!
Writer, Photographer, Car obsessive... 152 cars/22 years.
'07 Chrysler 300C Hemi Touring - Silver. Build 07/06. EVIC 4.12 2/27/06.
'98 Mercedes-Benz SLK 230K -Yellow + 528i Touring + 300CE
Given a choice between kids, or a V8... I'll take the V8.