If your truck has fender flares, there is a bolt in the rear bumper end's lower quarter.
If I remember correctly, three bolts attach each bumper end to the main bumper. These bolts are inside the bumper and a little tricky to remove.
You need a 12 mm and a 14 mm wrench.
I was just worried that I would have to get at something from the inside of the rear quarter. sounds like it is all under the truck. Correct