As has been stated a number of times many of the newer Class Cs are rated to tow up to the Ford 7,500# rating. What should also be noted is that many new Class As are not rated to tow anywhere near that much.
Assuming you come up with a MH rated to tow 7,000# , whether right from the RV builder, or after-market mods have been made to the hitch and frame extensions that would allow safely towing that much, another factor to consider is tongue weight. With 7,000# of horses and trailer you probably would have 10% (or more) tongue weight. That's 700# or more, added to the load on the motor home. That much weight would probably exceed the rating of a lot of rear axles, if not the whole GVWR. A properly adjusted weight distribution hitch would lessen that issue. Of course a weight distribution hitch should only be used on a MH whose frame and frame extensions have been properly "beefed up", to allow towing that much weight to begin with.