I'm thinking of trying one of these https://www.torpedo7.com.au/products/T7CATN04B/title/torpedo7-towball-mount-4-bike-channel-rack
I bought one a few years ago. Works well, good value for money. Ive mounted a post with a ball on top and fit it over the draw bar on the camper too. Keeps bikes off the roof, and not bouncing around out the back out of sight on the camper too.
Good points:
Quick to drop on the towball or remove
Locks to towball.
Fits most bike sizes, I've tried 29" MTB, roadie, 26" MTB, 24", 20" even a 12" glider bike, you do need to think about placement a bit though.
Downsides are:
Needs a plate under the towball that also prevents me from towing my box trailer without removing the plate.
No tilt option if you need to open the he back door of the car. Ok if you can access over the back seats.
Strapping the bikes down is three straps each bike, can take a few mins.
No very light and takes up a fair bit of space if you take it off the car and throw it in the back.