level tow bar

The slope should be no more then 4 inches from motor home DOWN to the the towed. Not a good way to tell how much drop hitch you need until you measure to ground from center of towed hitch and the motor home hitch. Use as little drop as you can get by with to prevent additional strain on the hitch.

Most makers tell you no more that 4 inches

You will need to measure both points and get the proper drop receiver

Your dealer should be able to measure the MH or a like one for you