How can I get more b from my trunk?

I have an 05' Grand Prix. I have 2 JL audio w6 subwoofers in a stainless steel ported box, powered by a 1200 rms watt mono d block hifonics amp. The trunk was dynamatted and a lot of the rattle has been eliminated, but I'm not getting much b out of the setup. The inside has insane b, but outside you can barely hear my system. What can I do to get more b out of my setup?