Ours had a 4" square bumper, but we replaced it with a
Mount-n-Lock heavy duty bumper for a couple of reasons.
1. We tried to use a bike rack on the rear bumper, but as many have experienced, the steel is so thin and the welds so poor that the bumper soon twists off.
2. I always had to take off the end of the sewer pipe to fit it in the bumper and wanted something big enough to store the hose with the end on it.
3. We could add multiple attachments to the back along with the bike rack. We keep a cargo tray and the spare tire.
4. It's nice looking, shiny aluminum instead of the drab painted black steel.
We took a 6,000 mile trip last summer up through Montana, Alberta and Saskatchewan and nothing budged.