Maybe do some research on wiring looms for the tow bar. I recently bought an NW Pajero and had an after market towbar put on at $690 from memory as opposed to $880 for the Mitsubishi one, bargain.

When I wired up for trailer brakes there's a loom goes in the front ($90) which is pretty easy to install and all plug in which is great. The loom at the back however is $380 or similar and has relays etc in it. I've presently tapped in to the wire for the trailer brakes at the back plug but would like to put the loom in to have it done properly. If I do, my "bargain" will leave me a couple of hundred $ worse off.

So, as I said, it might be worth researching what's included in the factory one from a wiring point of view.
Cheers
envee