Run any Cap's in that Van install? Couldn't see any and normally people make a feature of them if they go in.
I used to play about with Rockford Fosgate stuff, Punch 40's etc, Cerwin Vega.
I only really used to have two subs, a 12 or 15 and a 10, one for the low stuff and one for the tight fast stuff. You need the bass to be there in any SQ Car, but it doesn't have to be excessive unless your going for SPL.
Did try an 8 inch under the passenger seat with a 30 odd Hz baseline on test, ladies seemed to like it
I was more interested in quality than quantity, so it would be active cross overs, Mid/bass Mid and tweeters up front, DSP with a Mic to set the Image etc.
Used to make me laugh when the local boys would be really impressed about fitting their 6x9's (Or 7x10's if they were almost educated) in their standard, flimsy rear shelf in their Nova, standard speakers up front. "Yeah dude that's great, but...tell me, if you went to a concert, which way would you face?"
And running their Power, signal and speaker cable, all together done one side of the car...very entertaining.
Found a great substitute for Dynamat at work! Not quite as good, but cheap enough to double up if needed.