i just made my own mounting plate for a single din unit, moved the HU slot as far up as possible and mounted my subs remote gain and an on/off toggle and LED indicator under it. Its just some 1/8in steel bent and cut to fit, works well, even has room to mount a few more switches.
Ive played with the idea of a double din unit, its do-able in an XJ and the one in my friends JKUR is nice, but it looks out of place and it the touch screen kind of a pain to use. Im thinking about one of Fusions 700 series single din marine units for the next audio upgrade.
Not the best photo but you can see the HU and switch, the gain control is to the right and the LED to the left.