What's behind the pvc? I'm not quite certain what your wall type is?But if there are wood dwangs behind the pvc you could, first put up a batten between the two windows, and put track or pole on thatYou secure a narrow wood batten to the dwangs behind pvc, then secure track or poles right from one side of one window, through to the other window.Then it should support your drapes.
Gerald
January 2008