There is no way that a receiver should be just welded or bolted to the rear bumper.
I have a 2001 13
Scamp with a factory mounted rear receiver.
Scamp adds an additional cross member to the frame. They weld the receiver to the new cross member and to the bumper. The receiver sits below the bumper.
Unlike Floyds comment about "not the best idea on a 13 footer", I've had no problems for nearly 12 years of carrying my mountain bike and a folding chair on the rear of my 13 footer. I have had only had one or two occasions where the receiver did drag going in and out of a driveway. I could tell that the driveway was a little deep so I just took a little slower.
I rarely if ever pull my Scamp without the bike on the back. In fact, I think my only time was when I went to Alaska as I knew I wouldn't be using my bike. Having it on the back would add length and the ferry systems charge by total length so I saved quite a bit of money leaving the rack and bike home.