Exdwarfer, I have some limited experience with a rear rack. Jimtoo is right that it may void your warranty. I think that Heartland or Lippert stopped putting brackets on the frame for a bolt on reciever. Pretty wimpy, so just as well.
I copied a rack from fellow owner jnphobe. I fabricated the rack, then welded two recievers to the frame. One on each I-beam. It was strong and could support a bunch. The cost was about $250 for the steel, and my time. I sold that rig but saved the rack. I am waiting for a while before I put it on the new rig for warranty concerns. But it will be on soon.
If you need pics, just ask.
Just remember the warranty thing.
Peace
Dave