Since you are looking to sell it, you probably don't want to go all 'custom' on it. I had the same unit in my rig and replaced it with a standard car stereo. I made a custom box for it to fit the big hole.
I had to splice in the wires, but the old unit had a wire diagram on it, so it was pretty simple. I did have to wire the memory save and the on/off power wires to the same 12v source so it would not lose all the settings when powered off.. (remember, in a car you would wire the main power to the keyed switch and the memory saver to a constant hot source)
Anyway, you might try locating an Rv Recycler in your area and see if you can pick up a cheap replacement just for ease of install and sale..
Good luck!
Mitch