Lippert (the company that makes 90 plus percent of the RV Frames) make a series of Bike Rack and Cargo Platforms that go on the back of your 5er or TT. You can contact Iippert they will point you in the right direction and you can purchase direct from them.
Here is what Lippert says can be installed on their frames. I quote
"Outfit your RV with one of our quality and durable bike racks and receivers to take more fun with you on the road. Lippert Components builds an assortment of RV bike racks in a variety of sizes to fit many types of RVs. Should you need assistance finding a bike rack that will fit your RV, please contact us
. Our well-trained customer service team is here to assist you."
Here is a link to the Lippert webpage. RV Bike Racks & Receivers for Sale