Check over on ClubGP. I think I remember a breif write up on how to install them. Search for "roof rails" or "roof fences". Other variations my yield results too.
Marc
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'00 Trans Am WS6 w/ 25K miles - Lovin' it!!
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RIP '99 GTP w/ 41K miles - Totaled in fire
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RIP '97 GTP w/ 192K miles - Totaled when broadsided