They're not plastic, at least mine aren't. And while they are secured with sheet metal screws they are pretty stout. The original Yakima and Thule roof racks were always mounted on the drip rails - back when most cars still had them. On my '89 k5 I had the front Thule bar mounted to the drip rails and the back one was mounted to brackets bolted to the fiberglass that mimicked drip rails. I put both bikes and a canoe up there (not at the same time) and never had a problem. Still have some of the same parts and would not hesitate to install them on my burb if I had a need to. Of course if the screws had loosened or stripped due to rust or similar you would probably want to go a different route