What are the correct box specs to use in order to build a ported box to hold two 12" Rockford Fosgate P3s? The box has to be able to fit in a Mazda 3 sedan trunk. I included a diagram of the box I am using right now, but is it correct? It was built at a professional car audio shop in Toronto (Sidds Radio). My bass does not seem to sound deep enough, it is however loud. Is the box the cause of this? I need your help and suggestions.