I carried 2 bikes on the back of a trailer for thousands of miles. What I learned will apply to the back of a MH as well. Get a rack that the bike wheels sit on the rack. When the bikes hang on the rack with wheels dangling even with the best supports, they tend to make contact with each other and it beats them up. A rack with the wheel tray really helps keep them stable.
When you buy the rack, you will also need an anti-rattle devise. This is a clamping devise that takes all the play out of the rack/receiver connection. This will eliminate the "bounce" of the rack. You shouldn't get the bounce on the back of a MH as you do on TT but the anti rattle device is a must in my opinion.