I second this, and suggest you use the plastic push pins instead of nut/bolt/washer.
I installed mine with nuts, bolts and washers and it was on there solid. That was the problem though. I accidently bumped it, and because it was so securely connected to the bumper it ripped it off the bottom leaving a gaping hole where each of the front bolts were attached. Because I used washers, the holes that were left were huge, and mounting anything under there was pointless unless I got a new bumper.
Had I used the plastic push pins, there's a better chance that those would have snapped or released the lip, which would have caused less damage all around.