My scooter weight just over 400 lbs. I had a plattform made and a sliding ramp from under. I use a winch to take it up on the platform. Mine is a bit complicated since my scooter is a 3 wheeler, 2 in the front. You could have just one ramp and walk it up.
As for the hitch attachement, I went to a welding shop and they welded two receivers, one each side of the hitch. I figured if one hitch can handle 500 pounds, two would be just fine.
http://i651.photobucket.com/albums/uu235/Kidoo/DSCN9106_8337_zpsynazzb0b.jpg
Here is a guy that makes some different type, he is in Canada but you will get some ideas.
http://www.komocreation.com/specification%20produits%20anglais%202012.pdf