A lot depends on the RV and towed car
For example I tow a car that's about 4" lower than the receiver on the Motor home so I had Blue Ox build a custom drop hitch for me. It has both a 4" drop with a standard 2" receiver on it and on top is a "tongue" for a standard ball hitch. My bicycle carrier is one designed to bolt on in place of the ball.
They also make one that slips over the 2" square shaft of the tow adapter and clamps on..
OH I did add an "Anti-Rattle" clip also called a Hitch Immobilizer (made by blue ox)
One option is a dual receiver adapter usually one is straight through and the other is drop/rise.
If car and base plate and motor home receiver are same height you use the "Straight through" to the car and put the 2nd receiver on RISE and that's where the bicycle rack mounts.
If the car is LOWER turn it over
If the car is higher This will not work.