This is a recreation of the bottom bed roller (not side rail roller) of Apache Campers made 1973 - 1986. Made it based on dimensions taken from a “new” bed roller. For best results I would print this out of a durable material, PETG, Nylon, Delrin, something of that nature. I recommend printing the model with 100% concentric infill with top and bottom layers set to concentric. This makes for a very clean part. You can either print the part with supports for the bottom section and do some support cleanup, or print the core piece file first out of a material that doesnt stick to the material you are printing the main roller out of. In your slicer you would set it to pause at the layer just before it starts printing the bottom overhang and you would take the core piece with glue stick on both sides and put it in the cavity. If done right this results in a model with a very clean surface on the bottom. For PETG part I found a PLA core works well. For Nylon you can use PETG as a core.

If the model doesn't work for you you can change the scale of the model just by a little bit or change your slicer tolerance setting.

Model was tested with the original thrust bearings which measure to be 23.33mmOD x 12.83ID mm. New bearings that also work are the uxcell axk1024 23.60mm OD x 10.22mm. You can pick up a 6 pack from amazon for cheaper than your local hardware store. https://www.amazon.com/gp/aw/d/B0CJFRSVCJ/ref=ox_sc_act_image_1?smid=A30WUG2ZDGM0XM&th=1.