Here are a couple of pics to show my custom bike rack mod, although the bike rack is a Voyager rack made to be bolted(7/8" bolt) to a receiver hitch.
I do not wish to incite a debate about whether this should be done or not, and wish to state that this works, and that I can bounce on the arms of the bike rack with no problem. The Voyager rack is bolted(with a 7/8" bolt) to a 3/8" thick aluminum plate that is bolted to 2 pieces of 2" x 2" x 3/16" steel angle iron. The angle irons are bolted to both the c channel rear bumper and the forward c channel member ahead of it.
Rear view showing the rack, its aluminum plate mount, and the pieces of steel angle iron:
Ground view showing how the steel angle iron pieces are bolted:
The rear bumper alone is not strong enough to support much, but when additional support is added, like the angle irons, that attach to it and the forward c channel ahead of it, then the structure is strengthened overall.
The tool boxes are attached to both the rear bumper and the side members, and the safety straps are for additional safety.
Tongue weight is still quite substantial.
Good luck, and happy camping.