We started out with a bumper mount bike rack like you. Our son-in-law also. His bumper started cracking at the welds. We both went to a welding shop and had 2" receiver mounts welded to the frame. No more problems. When I asked the welding shop owner about simply reinforcing the stress points he laughed. Said " the welds will hold fine. The metal beyond the weld will tear/shear due to the constant twisting. Might be something to check if you are thinking the bumper can be "built up" to stand the stress of the extra loads. One of those better safe than sorry things for us.
FR Wildwood 22 RKS
2007 1/2 Dodge 2500, Cummins 6.7
Retirement training completed
Currently enjoying second childhood