I recently installed fiberglass French door and have attempted to stain them with a gel stain. All went well except for a small approximately 1"x3" area on the inner panel of each door where shipping brackets had been wedged in-between the doors and apparently rubbed the fiberglas smooth of any primer or pre-prepping and the stain does not want to adhere. The rest of the door is fine, with the exception of these two spots. How can I solve this--a prime? roughen the surface?