Hi Bob,
Although I've used hitch mounts on past motorhomes, I've yet to do that with my Unity. eTrailer is a good site to check for racks, the hitch mounted ones are here:
https://www.etrailer.com/dept-pg-RV_and_Camper_Bike_Racks-sf-RV_Hitch_Rack.aspxWhen I used them in the past the things to watch for are
1) Clearance to the rear of the motor home, my Unity rear cap does extend out a bit from the hitch, so you may need either a 4 bike rack or a hitch extender to get clearance as the last thing you want is to have the bikes rub on the coach.
2) If you have an rear access hatch, then a rack with a swing away / tilt down feature is really nice, otherwise you may find you have to remove the bikes and the rack to open the rear hatch. You may not have to worry about that if you don't have rear hatch.
3) A cover, wow-o-wow will the bikes get dirty back there !
Be interested in what you end up choosing and how it works for you.