I installed a bolt-on hitch receiver (around $50 on Amazon) and put a cargo carrier on the back and I use it to carry our 27 gallon portable sewer tank during travel (empty). I have an Explorer, so I didn't want to carry the tank inside the car or the camper.Or if we are going to a site that has sewer, I carry my coleman roadtrip grill on the cargo carrier. I haven't had any issues with it yet.
Based on what I're read, you don't want to put too much weight as the leaf springs provide little shock absorption and can put a lot of stress at the point of connection at the bumper. Say like a rear bike rack. I was originally going to put on of those on ours, but after some internet reading, I decided against it.