Hello congratulations on your purchase.I own a rtse challenger and found that the fiberglass rear window insert was installed with philips self tapping screws.After installing the insert a thin foam material was laid over the opening to cover the seam around the insert ,this way after the vinyl top installation the seam will be hidden.If you do not use the foam then it will show.The foam can be purchased at any upholstery shop,I used 3/16.Hope this helps.ps it also has an insert for the inside to cover the back of the fiberglass .