Planet Audio FU15/4

I am reinstalling my PA FU15/4 subs, I was using a 9 cubic feet box wth 4- 4" ports.  The box was divided and there was two ports for each sub.  The highest SPL that I registered was a 151.7.  Should I remove the divider?  Should I change the Frequency of the box?  I think the first one was tuned around 50HZ.  The Planet Audio website does not offer many options concerning box building.  The dealer I bought them from only said to put them in a large ported box (NOT MUCH HELP).  The previous enclousure had the sub's pushing straight up and the ports pointing up also.  The ports were at the back of the box near the back window.  I am using two MTX 1501D amplifers, this system will be installed in a 2002 Nissan Crew cab.

Thanks

Don't remove the divider as this will dramatically change the tuning of the enclosure(s).  Planet Audio's woofer spec sheets are at http://www.planetaudiousa.com/user%20manuals/2003%20Woofer%20Specifications.htm and their customer support phone number is (888) 990-1236.