No pics, since it was over a decade ago, but we built a couple of boxes for my YJ. The first was a bandpass design that held a single 10" sub.
Similar to this pic. We had it all squared off, and measured it to fit at deck height.
The second one, when I added another 10" sub, we just built a ported box and followed the angle of the back seat. The subs fired directly into it. Squared off sides, back, and top, with the angle up the front.
Similar to this one. The only differences being the width and angle. We used MDF and took several measurements to make sure the internal volume was sufficient for the subs.