Interesting that "Portakabin" is the test case...
Another one of those brand-becomes-generic situations.
The owner of the brand name usually proclaims that they don't want it to be generic, yet they gain massively from exposure and brand recognition as a result. If you wanted one of 'em, what would you google for? "Modular transportable building"? No, nor me.
They can't have it both ways...