If you want to put a subwoofer box in a Chevy Avalanche the chances are you'll have to build something yourself. The unique space constraints of the Avalanche cabin mean that most pre-assembled sub boxes will not fit. You can mount the box either behind the rear seat on the parcel shelf or on the floor between the rear seats and the front seats. Both have unique constraints and will fit a different size box, while one may take away passenger space.
Measure the space where you'd like to mount the sub. Record the measurements on paper.
Measure the sub you have chosen. Add two inches to the diameter and two inches to the depth in order to calculate the minimum size of the enclosure. Calculate the internal volume by subtracting twice the width of the MDF from each dimension and then multiplying the length by the width by the height. Compare this volume to the recommended volume from the sub manufacturer, which should be written on the sub's documentation.
Adjust the dimensions until the enclosure meets the recommended volume specifications and will fit in the space you measured.
Cut the sides of the box from the MDF using the jigsaw. Cut two pieces for the front. Draw the outline of the subwoofer on the front pieces. Drill a hole through the center of the outline, then put the jigsaw through the hole and cut out the rest of the piece.
Use the same method to cut a hole in the back panel for the terminal cup.
Assemble the box. Use the wood glue and screws to hold the sides together. Screw the large sides into the small sides for the strongest box. Use the silicone caulk to seal the box and to add extra strength to the joint.
Secure the terminal cup in the rear panel with the screws. Attach the speaker wire to the inside of the terminal cup and run it through the box. Connect the wire to the terminals on the back of the subwoofer. Put the subwoofer in place and secure with screws.
