This is what *can* happen:
![](https://rvrangerfamily.files.wordpress.com/2014/04/img_3322.jpg?w=723&h=542)
![](http://www.airforums.com/forums/attachment.php?attachmentid=145595&d=1321686984)
If you contact the factory, you are likely to find that a standard bumper is rated to carry only 100 or 150 lbs. It's not just the static load of the bikes that has to be considered, it's the additional dynamic load from the rear end bouncing up and down. Some TTs bounce a lot more too. I've read of some bikes being catapulted clear off a rear rack.
If you are going to do it, at least extend new steel back to the frame I-beams. Take a look at any TT brands that come designed for a rear rack like Nash and Keystone to see what they've done. Personally I wouldn't do it but many have one way or another. Alternatively, you could mount a bike rack up front in the A-frame like in the following pics. With the bikes up front, you can see them at all times too.
![](http://www.modmyrv.com/wp-content/gallery/mod-22-image-gallery/thumbs/thumbs_bike-rack-tongue-mount-1.JPG)
![](http://www.trailertray.com/uploads/1/1/0/0/11003812/809677_orig.jpg?363)