Masking tape is placed on the trunk edges where additional fiberglass will be applied. The tape will provide a barrier between the trunk and the fiberglass so that the panel can be removed easily. Pre-drill the ring to match the mounting holes in the subwoofer and attach T-nuts to the back sides of these holes. Apply Duraglas to the back of the T-nuts to keep them from falling out or moving. When using a large subwoofer with lots of power behind it, bracing the box to handle extreme vibration becomes very important. Cut braces from 31/44" MDF to bond the front and back of the enclosure together, as well as bracing the subwoofer ring to the enclosure base. With the carpet covering the front of the enclosure, staple the carpet to the subwoofer ring and to the amplifier plate along the rabbeted notches we created earlier. Quarter-inch upholstery staples and an air stapler work well.
After the resin-soaked carpet has fully cured, it's time to add additional strength. Apply five layers of 31/44-ounce fiberglass mat to the surface using more fiberglass resin. The combination of the resin-soaked carpet and fiberglass mat will create a 31/48"-11/42" surface thickness and a very strong enclosure. One final test-fit of the enclosure shows that we're ready to glue on our carpet. Keep in mind that you must maintain sufficient gap to allow for the carpet thickness, otherwise the carpeted enclosure won't fit in the car. Also notice the notch in the bottom of the enclosure to allow the stock trunk carpet to be reused without having to cut off the embroidered edge. Carefully attach the carpet to the enclosure, taking care to pull it tight to avoid wrinkles. Apply firm pressure over the entire surface with your hand or a roller so that the contact cement bonds together completely. Here in California, we have the benefit of year-round sunshine, which cures fiberglass quickly and evenly. In colder climates, using an electric heater in a small room or large cardboard box has the same effect. About an hour is all it takes to cure the fiberglass.Spray contact cement on the back of the carpet. We use the cheap Harbor Freight spray guns ($10 on sale) to do this, since they don't last very long with glue unless they're used frequently. Contact cement can also be applied with a brush, although it takes longer than the spray technique.