i just order 1 more fi btl 12 but not sure if it will fit. my trunk is long enough at 44 inchs width is the issue, at the tail end of my trunk it measures 57 inch in width for 23 inches in length then then the width narrows down to 32 inches width. i need help.. the height of my current box with 1 btl is 15 inch

The problem you are going to run into is the ability to put the sub box into the trunk..unless you decide to build it in the car.

Im sure you could make it fit, but its up to you to be creative enough to pull it off. That's the fun part anyways, it may take you weeks to get it right but anyone can