Your 2007 Jeep Commander is an excellent example of the new style of vehicles that car rack manufacturers are cranking out and forcing car rack companies to redesign new systems to fit them. Your Jeep Commander doesn't have crossbars and it doesn't have usable side rails. You're right that normally you can just attach the
Thule 450 CrossRoad roof rack system or the
Yakima LowRider roof rack system to a pair of side rails. They just clamp onto the siderails. But the Jeep Commander has this solid raised rail as I'll call it. So you can't mount one of these racks and you can't use a style of roof rack that normally mounts to a naked roof top such as the
Thule 400XT Aero roof rack system or the
Yakima Q Towers roof rack system.
Thule Racks is currently the only company that has come up with a solution for this issue. Vehicles such as the 2007 Jeep Commander now include fixed attachment points on the roof that Thule Racks has taken advantage of. They have released the
Thule 460 Podium roof rack system which will mount to these attachment points. The Thule 460 Podium uses a new style of Thule Fit Kit to work with these attachment points. The Thule 460 Podium Fit Kits are actually specifically designed plates the attach to these fixed attachment points on many new model vehicles. You will use the Thule 3040 Fit Kit on your 2007 Jeep Commander. These four plates mount to the attachment points on the siderails and then you connect the four Thule 460 Podium Feet to the FitKit plates. A pair of Thule load bars mounts to the four 460 Podium Feet and you now have a super solid multi-purpose base rack system that you can then mount any of Thule Racks gear carriers to.
The Thule 460 Podium roof rack system is a complete base rack that includes the four 460 Podium Feet, the four FitKits and a pair of load bars. Thule Racks also makes the
Thule 460R Podium roof rack system to fit the Jeep Commander. This is essentially the same as the regular 460 Podium except that it uses the elliptical aerodynamic load bars instead of the classic square Thule load bars. You would still use the same Thule 3040 FitKit with the 460R Podium version.
FYI, any of Thule Racks or Yakima Racks gear carriers would attach to the 2007 Jeep Commander factory rack crossbars if you had the factory rack crossbars already installed. If you don't already have them installed there's really no reason to go with the factory cross bars, as they would cost as much as the Thule 460 Podium setup and they aren't rated to carry as much weight as the Thule bars.