I have a 05 impala and my custom 18 by psi. Im building a box thats 34wx30dx14.5t. 6.9 cu ft. Sub up slot port to the rear of the car. Im wondering what the best way to brace the box is and in what locstions. My amps change alot but ill be giving it between 2500 and 3k rms daily application. Any extra input on this would be great.