Installers that have had to build a custom tuned enclosure for any style Mustang between the years of 1994 and 2004 know that getting the box inside the trunk is the hardest part of the job. In this article, we will be showing that you can build a box that slides underneath the rear deck, leaving the customer with a small amount of space to fit probably a bag or two of groceries. When designing any type of enclosure, you must always take into consideration the customers’ needs. In this vehicle, trunk space is very limited so the customer will need as much space as possible. Because the distance from the trunk floor to the metal trim piece behind the rear seat was only 12 inches, this dictated the maximum external height of our enclosure. Also, the width of the metal trim was 32 inches, meaning the box could be no wider than 32 inches. This box design meant that the enclosure would have to be slid in from behind the rear seats.