There are many posts on this issue.
In summary, some people do have bike racks on the back, but most have a hitch attached to the frame of the TT and not a bike rack attached to the bumper. Most TT rear bumpers are weak and there are many horror stories of losing the bikes, losing the bumper, and potentially injuring other motorists following behind.
The over the tire adapter looks incredibly unsafe to me. I don't know if I've ever read a post about someone who has one, but I haven't really looked because I would never choose that option.
Some people have posted that they've had good luck with RV ladder bike racks, but others report the ladders pulling loose. It may be a function of tightly securing the bikes to eliminate bounce. I personally wouldn't risk it.
In my opinion, the only real and safe options are:
RV factory installed and supported rear bike rack.
Rear bike rack attached to a heavy duty hitch attached to TT frame.
Over the tongue bike rack - either by Arvika, or Bike Bunk/Trailer Tray, or homemade knockoff as shown in the mods section of this forum.
Of course you could also carry on the TV roof or truck bed, or simply haul inside the TT itself.