First you need to verify you don't exceed the GCVWR of your motorhome with the trailer attached.
Second, either the hitch can be reinforced or a new one built to handle the weight by a reputable welder/hitch installer.
On my 94 Marquis Le which had a poorly built factory 5000 lb hitch that I wouldn't have towed anything with, I choose to replace it with a custom built one that would handle even the stacker you have. With my 24' enclosed Pace Shadow GT and race car and tools etc, I am very close to my GCVWR, but am not exceeding it. The bus doesn't even know its back there.