If this is a metal box like a shipping container, you'd have to attaching it to the outside somehow. However the website just says "steel framed" which suggests the sides might not be metal, in which case it might work.
However it's quite possible that something else happened to it that they don't want to admit. Like maybe their driver was DUI and crashed it.
PODS are advertised as having a transparent roof for light, most likely polycarbonate. Not sure if that would be sufficient for an AirTag signal if the rest is metal, but I suspect it would be.