We have a rear mounted rack, not on a bailey, but on our soon-to-be-sold Sterling Espace. It was installed by the original dealer, with extra strengthening in the back wall of the van to take the load.
As far as stability goes - our outfit was quite well matched - just about 85% weight match, but I would say that putting bikes on the back rack did affect the stability, noticeably, but only a little. On a windy day I would definately feel more lateral movement of the van, and when being passed by heavy vans etc. More so if the van itself was heavily loaded. Taking things easy and keeping an eye on the weight of the bikes helped - in the end we only put our lightweight road bikes on there, and put the others on top of the car with roof bars. We've just changed caravans, and I'll not be putting a rear mounted carrier on - I just don't really like the idea of putting weight in the worst possible place, despite the convenience of it.
Quite often, like last summer in france, we carried the bikes on the car roof when on the road, but then used the caravan's rear rack as a place to stash the bikes when we're not using them while on site, or going out for the day or whatever - they can be locked to the carrier - worth it if you have expensive bikes.
Probably just confused things now, but I would say that if you can put the bikes somewhere else, do so. Probably on the car roof.