Why not just use a hitch mount, and keep from drilling into the hard cover. Keep in mind these are fiberglass covers and could start getting stress cracks from the vibration of wind buffeting along with chasis vibrations. Boats get them all the time.

I have an A.R.E whichare pretty thick and heavy painted to match the truck, and even though they have one as an option, I wouldn'tdo it. I use a Thule hitch mount.