As for where to get it, you can find it on Amazon. (Amazon.com: Pro Rac Systems Inc. Tent Trailer 4 - Bike Carrier: Automotive
). It IS
expensive, but it is very well constructed and a practical way to mount 4 bikes (or six if you get an extender). Note that it does add weight
to the tongue however. I use a WDH so I was less concerned.
You'd definitely do not want the rear tire resting on top of the windows - bubble type or not, but you can adjust where the rear wheels "land" by how far forward you attach the front to the tongue frame.
The rear wheel shouldn't slide, because you tie it down tight with a pair of straps. The rack kit also comes with some invisible protective film that you apply to the RV where the tires rest so that it won't scuff the top. I haven't put them on yet as I won't be camping with bikes this weekend. I'll probably do so next weekend, however. There is also an option for some pads you can attach for the rear wheel, but I don't know how useful they are (ProRac Tire Pad Kit (2 tire pads): Amazon.com: Sports & Outdoors