Keep in mind that it wasn't long ago that titles/registration were not even required for truck campers and shells.
There very well could be places in the US that still doesnt. I dont know.
I do know that it wasnt until the last few years that Idaho started requiring them to be registered.
But even then, units without titles were grand-fathered in.
There are lots of older units out there that do not have titles, and potentially not even a dealer ID plate.