Vehicle specific matched Subs/Enclosure

[12V71]

I know there has to be an equation somewhere to specifically design how many and what size sub woofers are used in the volume of a particular space. I understand this plays an important role since the area available is the enclosure in which the speakers function.  I have a Dodge dually extended cab with 4 Rockford 12s (prime r2d4) that I have never been happy with (a contributing factor is the prefab ported box) They are facing backwards and ports are as well. I could cut the box down, remove the ports, and end up with a sealed box built to the intended specs but, that would be to simple and cost effective. Instead I would like to replace them with something better and possibly more suited to the area (cu ft). Available Dim. length 62" width 18" height 14" for reference. (ref) Power 1000 watts in 2 ohm via Kenwood KAC-9106d.  Budget is best value (meaning that double the cost to due 10% better is out)