If you are writing to Joe Soap who is lodging, staying with or visiting John Chalk at 123 Main Street , it would be, and still is, perfectly correct to address your letter to
Mr Joe Soap
c/o Chalk
123 Main Street
In fact this would have been essential if Joe Soap had been staying in a flat in a tenement block where all the flats shared the same street number, otherwise the postman wouldn't know which flat to deliver the letter to.
I've had things sent to me c/o friends, and on occasion c/o a hotel, as recently as last year.