This might be hard to explain with out drawing or talking it out but i will try to make it out.
Has anyone made a box that is like two boxes facing each other with mdf that goes over the top and bottem and back of the two boxes with the subs facing the inside. (basiclly the subs will be firing at each other and and it will be like a tunnel with the opening towards the from of the car. i was gonna try this in my trunk but idk how it will sound it was just an idea. If this dosent make sense i will draw it out and try and upload let me know thanks.