May be late to the party, but I have 3/8 angle iron full length behind my bumper. The tow bar mounts are bolted through the bumper and into the angle iron. Anlge iron is notched around the frame rails. This has provided me with 7 years of no hassle towing behind my Class A.
On the YJ I bolted directly to the bumper and towed it to Florida, Northern Ontario, all over Michigan, etc. No hassles, no problems. Better bumper.
I have no discernable flexing or distortion from towing this way. If I think about it, I should snap some pics to show the set up. See if I can get behind the bumper to see the angle iron.