I'd love to design a decent sub into it, but I don't really have anywhere to put it. I would lose functionality because the seats fold down and I can put long stuff from the boot right though to the front, it's been really handy. One place I thought would be okay for a sub would be to build a box just behind the center console... that way I would only lose the seat in the middle.
I installed a tow bar a few weeks ago and am looking around for a trailer, but I would really love a single cab ute. I haven't decided fully what would suit me the best, at the moment I'm thinking commodore or falcon ute.