Back of the Box

• 1). Remove everything from your trunk and thoroughly vacuum the trunk's carpet. The carpet should be left in place to ensure a proper fit for the subwoofer box.
  
  
• 2). Cover the area in which you will be building the subwoofer box with a few layers of heavy masking tape, extending it 3 to 4 inches past the desired size of the box. You should include the floor and side walls of the box.
  
  
• 3). Add a layer of aluminum foil over the masking tape, using additional tape. This will provide another layer of protection to make sure that none of the fiberglass resin soaks into your trunk's carpet.
  
  
• 4). Draw the outline of the subwoofer box onto the aluminum foil with a marker. The bottom and side walls will all be one solid piece, following the natural curves of the space, and should be drawn as such.
  
  
• 5). Tear fiberglass mat into 5-inch squares. Tear more than you think you will need. It's better to have too much than too little when you're halfway through the project.
  
  
• 6). Mix a batch of fiberglass resin with its catalyst according to the mix ratio provided in the instructions.
  
  
• 7). Brush a layer of catalyzed resin onto the tinfoil, extending it slightly outside of the marker line.
  
  
• 8). Lay fiberglass squares into the resin, overlapping them slightly and covering the entire space within the marker line. Don't worry if the squares extend past the line a bit.
  
  
• 9). Tap more resin into the fiberglass with the paint brush, saturating it fully and forcing out any trapped air bubbles.
  
  
• 10
  
  Add three more layers of fiberglass and resin.
  
  
• 11
  
  Allow the resin to fully cure. It will take at least two hours before it hardens and is no longer sticky to the touch.
  
  
• 12
  
  Remove the subwoofer box, aluminum foil and tape from the trunk.
  
  
• 13
  
  Trim off the excess fiberglass with a rotary tool, following the marker lines.
  
  
• 14
  
  Drill a hole in one of the walls large enough to pass the subwoofer's wires through.
  
  

Inside of the Box

• 1). Cut a speaker ring out of MDF. The inner diameter should match the subwoofer; the outer diameter should be an inch wider.
  
  
• 2). Cut four wooden dowels to act as legs for the speaker ring. The length will depend on the size of the box, but the rear legs should be about an inch shorter than the box height. Cut the front legs even shorter so that the speaker ring sits at a downward-sloping angle.
  
  
• 3). Glue the legs to the speaker ring, forming a table.
  
  
• 4). Glue the speaker ring "table" into the subwoofer box, with the lower end facing out.
  
  

Front of the Box

• 1). Lay a tarp on the ground and set the subwoofer box onto it.
  
  
• 2). Drape a piece of fleece over the entire box.
  
  
• 3). Glue the fleece tightly over the speaker ring (like a drum head), then out to the walls of the box. Wrap it around the edges and glue it in place to the back, maintaining the tension. Work out every wrinkle in the fleece as you glue.
  
  
• 4). Trim off any excess fleece. You should now have the entire front covered in a layer of fleece.
  
  
• 5). Mix a new batch of fiberglass resin and catalyst.
  
  
• 6). Brush a layer of catalyzed resin onto the fleece. Don't add any within the speaker ring; this will be cut out later.
  
  
• 7). Build up four layers of fiberglass mat and resin, following the steps outlined in the first section. The first two layers of fiberglass should wrap around the back to connect the front and the back. After those two layers, only glass the front of the box.
  
  
• 8). Allow the fiberglass to cure for at least two hours.
  
  
• 9). Cut the hole in the speaker ring open with a rotary tool.
  
  
• 10
  
  Sand the outer surface of the subwoofer box until it is smooth.
  
  
• 11
  
  If desired, paint the subwoofer box.
  
  
• 12
  
  Put the box back in the trunk and thread the speaker wires through the hole in the back.
  
  
• 13
  
  Press the box in place. It should fit snugly, but if it doesn't you can glue it to the trunk's walls and floor.
  
  
• 14
  
  Wire the subwoofer and screw it into the speaker ring.