I saw this while we were on our last trip. This guy made his own bicylce rack which is attached to the king pin on the fifth wheel. We throw our bikes in the back of the pick-up (nice to have an 8 foot box), so it is of no use to us, but I thought I would share this in case someone else can glean something from it.
2012 Cruiser Sahara 330SS
2015 F250 Super Duty diesel
For those not wanting to make their own, Arvika from Quebec makes a great fifth wheel rack that attaches to the pin box. I have had one for several years and love it. Call Arvika and ask for Guy. He will make sure you get the right model for your rig and for your needs.