Steve, the closest people in the U.S. to your "travelers" might be migrant farm workers, who aren't all from Mexico and other foreign countries (especially in the eastern U.S.). I don't know how many have fixed addresses part of the year.

There used to be socially recognized classes of peddlers, tramps, hoboes, etc., but I think very few people do anything like that now.

Richard, if I've got this right, American copyeditors often follow a suggestion that Fowler made on "that" and "which" (that is, they don't allow "a suggestion which Fowler made"). However, most Americans don't make this distinction, as standard British usage doesn't. "That" is commonly used for human beings here. I didn't even notice that Dick had used "who" in one clause and "that" in the next.

I take it a British caravan is an American trailer/mobile home/camper/RV? (Not that those are exactly the same thing.)