thanks so much for that extra description and picture of the hidden bolts.Install went fairly well, no problems. Another reviewer on Amazon mentioned that the hitch covers up the center bolt on the underside. Having read that, and noticing that the cover 'notches into' that bolt, I unscrewed it a bit and left it in. When the cover went back on, the notch on the cover just slid into the gap. I doubt it will stay tight, but there might not be any room for it to fall out anyway. It is not a vital part of holding the bumper on, so no biggy.
One has to pull the wheel well plastic forward and out from under the cover to reveal the hidden bolt on each side. Attached is a picture showing where it is when the bumper is off.
I did not install a harness, as I do not plan on towing anything. I just use a cargo basked of sorts for additional room (firewood, the odd kite buggy, etc). But I can see where the harness would come out through the inside of the bumper support, and through the hatch in the cover.
Contact me if you have any questions. Cheers