On the subject of a cargo carrier mounted to the tire carrier hitch, not only is the hitch too weak for that but you increase the risk of jackknifing your rig with all the extra weight in the rear end. Case in point, our neighbors own an enormous 38ft.-10,000lb travel trailer. They own a welding shop so the husband welded up a very nice rear mounted aluminum cargo carrier. Then he loaded it up with Honda 3000w gen., utility box, fire wood, fire pit, tool box, chairs, etc.
On the way through Banning Pass he caught a cross wind that pushed the rear of the trailer sideways AT WHICH POINT IT WHIPLASHED SEVERAL TIMES ACROSS ALL 4 LANES OF THE I-10 FRWY AT 80 MPH! Yea, he always tows that fast and pays no attention to the California vehicle code whatsoever. He came within a whiskers width of jackknifing his $50,000 rig and needed to change his thoroughly dampened underwear after finally getting things under control. Now he owns a 100mph speedboat, what could go wrong?