Don't do it, they are junk. I had them on my car for a few months, they stick out and IMO look bad. They cost $70 + shipping from LRS. Instead, spend $20 on 240/320 grit sandpaper, filler primer (or bondo if you have large cracks), new window seal, and some black trim paint.
Then all you need is some time and elbow grease. You will be much happier with the results. I just did mine a few weeks ago, here's a thread.
Fox trim restoration - Sandhills Mustang Club Forum