I don't know if you're looking for a multiple sub setup, but here is my single sub setup. The passenger seat is functional and one person can ride back there about as comfortable as can be expected in the back seat of a Ranger.
I can't remember the internal volume of the sub box, but I think it's ~1.5 cubes. Pretty basic but it works well and the seat can go all the way back and recline way beyone usable/driveable.
whoops, I see you have two subs! Oh well. Good luck