Best Bass for SRT-4

My brother and i own walkercustomdesigns and every year we try to bring something new to are local festivels and this year we are going with 1 HK15x2 MA and we are going to glass it and paint it and all that good stuff. Our question is, what can we do to get the best bass inside the car and out with a singal sub? I know now with my 2 12 MAs it sound way better when the back seats are down. I don't want to have to keep the seats down when we do the new sub. We were thinking of sealing the trunk off and then cut an opening in the back lid to allow the pressure to come into the cab. If we decide to do this what are the best methods? It will be 1 sub facing the trunk and flush to the contours of the trunk. What is the best way to construct a port (slotted) in a glassed box. Any help would be great. Thanks

First I would experiment with sub placement.  Use any sub and move it around in the trunk and see where you get the best bass (from the cab).  Usually this is towards the extremities of the vehicle.