I am just running a single 10, and a smaller amp. There was plenty of room for my amp, but I doubt that big amp in R.J.s jeep would fit under there let alone allow for air flow. There is nothing under the body where the rear seat is, and I have seen a few set ups where guys have used a hammer to "make" a little more room for a bigger amp.
I would like to find a pickup style box for my sub so it takes up less room. It won't sound as good, but it will give me a lot more room in the back.