I painted a fibreglass bumper on an old car before after a car park bump cracked it and put a small dent in it, just sanded back the repair, filled with cataloy (isopon P38), sanded back smooth again, then just painted as normal - primer, colour, clear with sanding in between (multiple thin coats of each stage too).
looked fine when it was finished, and was still looking good when I sold the car, but I'm not 100% if that was the correct procedure or not, sorry.
looked fine when it was finished, and was still looking good when I sold the car, but I'm not 100% if that was the correct procedure or not, sorry.