Towing behind 5th wheel

[kayakterp]

those bumpers are usually not made to hold more than 100 lbs.
That's barely enough for a spare tire and nothing more (except the sewage hose lol)
Even a bike rack is a big NO-NO

 

[Joe Hogan]

If you want to see an example of an over loaded bumper on a 5th wheel, see the video. He had three bicycles on a rack attached to the 5th wheel bumper and it failed.

 

[FL-JOE]

IMHO you would have to weld a large support system off both main frame rails coming back, then weld on a receiver off of that. Even constructing all of that if you put too much tongue weight on the ends of your main framing and cause a little flexing you could easily cause cracks or spiderwebbing on your rear cap, or the rear body portion of your fiver.

Of course there are other obvious reasons not to tow the way you are wanting to also. You can't back up a combination like that, or at least not more than 10' or so. If you swerve in an emergency there will probably be zero chance of recovery and you will crash. If the total length of that combination is over 77' or so you will have all types of issues parking even in interstate rest areas because you will be longer than commercial big rigs.