I have a 1963
Bambi. The rear “bumper” is just a piece of “C” channel, that serves as a crossmember for the frame.
I have seen pictures of Airstreams with modest rear chrome bumpers that must be custom. Nothing overly fancy, but generally rounded to the curve of the back end and chrome that can be polished like the rest of the trailer.
One pic the comes to mind looks like Basic rear bumper off an old Volkswagen Beetle maybe 3 welded end-to-end with a couple beetle bumperetts on the corners
Is there a vendor in the hobby that makes a simple chrome rear bumper ? Or if I welded one together, could is there somebody that can Rechrome it ?