I didn't know that! We had an 89 Cherokee that made a lot of boxes for, not for testing but showing off.
Port back subs up always worked well for us in it. We never tried port to the side.
OP if you need a box design, or want one, I can do one for you. We can try out hispls advice as well and maybe side fire.
@hispls, that is a great idea to side fire a port with the box all the way against the hatch. I've done a ton of side firing in trucks and trunks, but not quite as much in a SUV.
All downfiring also works well if you're space limited on where you can put the box.