1987 Southwind towing capacity

Those ratings have to do with how much tongue weight placed on the rear of the coach. Gas coaches are notorious for having poor tow ratings. The reason for this is most RV manufacturers use frame rail extensions that are either bolted or butt welded onto the end of the chassis manufacturer's frame. This is a very weak way of attaching the extensions. The other issue is gas rigs are usually at or near their GVWR given they are essentially limited in torque. The Chevrolet 454 which became the Vortec 8.1L is a great engine. However, it simply doesn't have the torque of a diesel. Back to your situation weigh distributing hitches force some of the tongue weight forward onto the front wheels reducing the unloading of the front suspension. A very light front suspension and nearly overloaded rear suspension is extremely common in gas coaches. If you have a weight distributing hitch which you can tell because it has spring bars and a large head then it levels out the weight between the trailer and the motorhome. Gas motorhomes typically have a very long rear overhang exacerbating the problem. Since you are intending on towing a car behind your motorhome on a dolly you will be fine because it essentially has no tongue weight. In this case you can use the "Weight Distributing" rating of the hitch. Keep in mind that you could not tow the same car on an auto transport that did not have a weight distributing hitch. So in short you should be fine towing your car in the manner you describe. You however MUST have a separate braking system either on the tow dolly with electric brakes or if you flat tow on the vehicle itself. In most states this is a legal requirement. Your motorhome's brakes don't have the ability to stop 4K extra weight in the back. If the tow dolly has electric brakes you will need a brake controller in your MH if it has surge brakes you won't need the brake controller.