I agree with the other poster on the use of the Anderson hitch for towing a 5er. Like I have said in the past do a "FREE BODY DIAGRAM" on that hitch with the loads that the hitch see's from your 5th WHEEL. Once this is done and you see the forces that are present you will/would never tow with the Anderson hitch.
The load input for the Anderson hitch is at the top of the hitch ball and it is offset either to the front or back of the center hitch ball in the bed, depending on mounting of hitch. Now you transfer that load point from the top ball to the lower ball plus the bending moment that occurs, as this load is pushed down around the top hitch ball and this is what is causing your bed to deform.
What I see happening is this bending moment is causing the bed to be deformed in front as the hitch is pushed down. The loading of the 5th wheel as the load is stopped. At the ball joint towards the rear of the ball, I bet you will find that this has been slightly deform as well. The sheet metal might be slightly raised, not visible to the naked eye. But put a straight edge at this spot and it may be higher at the mid-point than the surrounding metal.