Those are nice lights. With the 4 tapped holes in the back of the light you could mount them right to the bumper. Picture the lights mounted on the rear face of the bumper out at the ends by the rubber caps. Drill through the bumper and use short pancake head screws that you can install from the inside using a stubby phillips. The shallow heads won't interfere with the sewer hose.
If you would like or have any use for the 4 1/2" square U bolts that I used in my first installation, I would be happy to send them to you for free if you have a use for them, they are still pretty clean and rust-free.