You may find this interesting:
There was a posting in March, 2015 dealing with the Keystone pull out bike rack. "Open Roads Forum > Fifth-Wheels > Cougar rear bike rack"
General consensus was to watch for the added overhang at the rear of the coach as it could create some issues.
I have one on my 2014 Cougar 327 RES and other than using it to store equipment off the ground when parked I do not pull it out when traveling because of the overhang issue.
In viewing the photo on the response I wonder how long it would take to scratch and damage the bikes if you just tie then with a bungee cord? I'm sure that you can design a better system but you are likely left to your own device.
Good luck and enjoy your new trailer.
GPG