Before adding belly pan:
Metal framework that it attaches to:
Belly pan cut out:
..and attached:
I've since added another four screws to hold it more firmly in place. It is fastened with 1/4-20 screws, fender washers, and spring nuts.
I'd like to find a clean way to cover the tow hook holes as well, but I haven't figured that one out. I want to be able to clip a cover in place and be able to remove without reaching around the backside of the bumper.
-Mike