Aine - I do it exactly the way Kat describes. They will adjust quickly as long as they feel safe. Sign on the door is critical. I had one particularly stupid moving man open the door and the cat went into the fireplace and up the chimney. I ripped the sleeve out of my blouse to get her by the tail. The idiot stood there laughing further traumatizing the cat. Then I had to board a flight with two angry cats and a torn blouse. KEEP THE DOOR CLOSED until all strangers have left and you can go in an reassure them. They'll be fine.