Here's some pics of my setup.
First two are just to reference how the seat looks
Here is the box. Got it from the local car audio store for 40 bucks, they told me if they made me a custom one it would be about 100. So if you're getting quoted at 200+ like some have stated in this thread shop around! This box is 3/4inch mdf. Houses a 10inch, has a center depth of 6inches (keep that in mind due to the depth of the sub). top depth is about 4inches and bottom is about 9inches. And it is sealed, the sub is a W3v2. Oh and the amp actually fits under the passenger seat. I could put the seat back a little further if I had a grill on the sub, but as it sits it would hit the back of the seat, which isn't a big deal cause the back of the seat has some play, but it just makes a funny sound, where the grill would naturally push the back of the seat in and the sub wouldn't hit it.
I also hammered nails into the box from the inside out and bolted the box to the floor and back. Have fun stealing this bitches!
Here's a link if you're interested in swapping in these seats:
Extended cab split bench into regular cab.