How Do You Knock Out A Fiberglass Box? When it comes to durable, lightweight, and versatile storage solutions, nothing quite matches the reliability of a fiberglass box. Whether you’re outfitting a boat, upgrading a truck, managing electrical systems, or repairing a vehicle roof, fiberglass boxes are essential components across a wide range of industries. But what happens when you need to modify one? How do you knock out a fiberglass box safely and effectively without compromising its integrity?