unless you have a very large motorhome (like a diesel pusher) , I would not advocate carrying anything (including a scooter) over a couple of hundred pounds on a rack.....(weight of) rack + scoot + pivot point of rack relative to centre of rear axle (creates a teeter totter) = too little weight on front wheels and too much weight on rear wheels with a high potential for trouble....we have a 34 ft motorhome with a chassis capacity of 22,000 pounds. We use a 5 ft X 8 ft landscape style trailer with a 4 1/2 drop gate and a tongue box for all the straps etc. The box also keeps stones etc off our scoot which is perfect....
If you want to test the water, take your RV over a scale capable of weighing each axle. you might be surprised at what you find...
Take Care