When I purchased my 07.5 dually I purchased just the frame mount. I used my existing Signature 24k Reese. Reese has re-inforced the underbed rail mounts and now use 2 large plates that bolt around the frame. When the hitch and me left the installer they were tight. Once I hooked to my 5er and went around the block I was scared to death I would not make it home from the movement in the hitch. When they made the install I black spray painted the frame and plates and it was obvious that the plates were moving.. We re-tightened the bolts and the installer assured me they would be OK. Well as you all know when something is moving under pressure it can cause problems. My son and I came up with a fix. Please look at the photo closely. We made NO welds on the frame. We welded the frame plates and the axle bumper support together with a 1/4" x 2.5" x 11" plate..

 

Make it a habit of checking the welds often.
The frames do flex and that will put a lot of fatigue at the area of the welds.