I put this clamp on my receiver and it stops the bikes from flopping around, I think the movement would help a week bumper fail.
https://www.walmart.com/ip/2-Hitch-Receiver-Tube-Stabilizer-Reverse-Anti-Tilt-Locking-Collar/29389983?wmlspartner=wlpa&selectedSellerId=1201&adid=22222222227020073589&wl0=&wl1=s&wl2=c&wl3=52571299871&wl4=pla-84453160871&wl5=9032873&wl6=&wl7=&wl8=&wl9=pla&wl10=112561859&wl11=online&wl12=29389983&wl13=&veh=sem&gclid=EAIaIQobChMI566hm6zm3gIVDyCtBh3CgQNREAQYBiABEgLdTvD_BwE
Having said this I still want to redo the back bumper to carry my KLR and move the bikes to the front receiver.