We use custom built bumper assemblies to support our back blades for snowplowing. The brackets for these steel bumpers are configured to bolt to the side and bottom of the frame rails. We also have some reinforcement for the tow hitch which eliminates access for the spare tire carrier.
Back blade applications put a tremendous amount of stress on the frames, but haven't ever seen a failure in our fleet of 1/2 and 3/4 ton Dodges. Can't say the same for the GM products.
Andy