Possible Clues:

• Vehicle that is used for cinema advertising
• Start to complain and return caravan from U.S.
• Creeping plant in caravan
• Home on wheels
• One who's behind a short film
• Forthcoming-attraction ad
• One comes before the big film, and one comes after
• Before the picture, behind the car
• Promo, of a sort
• Off-the-set living quarters