I fitted a purpose built rack to the rear bumper mounts on my 2011 Swan - if I take the front wheels off the 2 adult bikes, then they do not interfere with the slide of the rear bed so I can leave the bikes in place if only stopping for 1 night. The only issue is that I had to remove the spare wheel so this travels in the boot of the car.
I have posted photos of the set up somewhere on this site and will try to attach a couple again, but my PC is not doing what I want it to do...!
So far, no problems of the bikes moving - but I would be cautious of fitting a standard rack to the rear that would allow the bikes to 'bounce'.
Paul