The black plastic is decorative, not functional. So you will not only need cross bars, you need the OEM roof rails the cross bars attache to. Several altitude owners have discovered this to their dismay, and there have been quite a few threads on the subject. If I recall correctly, you have choices that range from cross bars that clamp to the door/roof to installing the OEM rails. Jeep sells the rails in their accessory catalog. The cross bars are a thule design, and many of their components fit. There have been quite a few discussion threads. Anyway you do have some choices.
The PITA of installing the OEM rails is that four fasteners need to be drilled out and replaced. I've read recently, however, that you can fit the OEM rails without that hassle because leaving the end fasteners loose enough to slide the end caps on works perfectly. The rails themselves are solidly bolted to the roof using the existing fasteners and the end caps are held securely in place by the rails.
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