6. The center of the box got a double dose of ½-inch MDF down the center and the open ends of the ports were beveled with additional pieces of MDF. The interior corners were smoothed with body filler to create a fillet. 7. The ¾-inch MDF was used to create the rings for the square Kicker subs. They were positioned carefully to ensure symmetry and to keep plenty of clearance for the cones. 8. Fabric was stretched over the box and stapled into the frame. We’ve seen shops use fleece or jersey, the same material as a T-shirt. It will provide the contour of the box and keep the curves equal on both sides. 9. The outside of the fabric was coated with a thin layer of epoxy filler that’s easy to sculpt into the exact shape. It was allowed to cure overnight.