When dealing with structural body panel on a vehicle, it is best to use metal panels for strength, quality and alignment of body panels with no defects. You will find, most high end quality custom fabricators use metal whenever possible. However, there are those back yard fiberglass guys on ebay that will always sell fiberjunk for a cheap price. And here is the problem with using fiberglass on sectioned body panels...Front Fenders are attached to the vehicle in 3 separate areas. 1. The fender screws under the hood, 2. the Fender screws in the door jam and 3. the bracket to the front bumper. The problem with this is, as the vehicle moves, body rolls, goes over bumper, etc. it causes friction and tension that has to release, because the fender is being pulled from three different points. Thus what happens as a result are hair stress cracks that allow air to enter the fiberglass. Then the sun bakes the paint and material under the paint causing the cracks to break through the paint and causing the air in the cracks to lift the moisture through the paint and cause paint defects, cracks and bubbles. You get what you pay for. Depending on the preparation before painting and the environmental climate the vehicle is exposed to, the cracking and defects will come through from 2 months to 8 months. Bumpers and Wings are fine in Fiberglass as they have no pull and stress at multiple points however body panels like fenders do move and roll will the chassis.