Advertising vehicle? (7)
I believe the answer is:
trailer
This clue is a double definition.
'advertising' is the first definition.
(trailer is a type of advertisement )
'vehicle?' is the second definition.
(trailer is a kind of vehicle)
(Other definitions for trailer that I've seen before include "One comes before the big film" , "Short scenes from a future film" , "Film preview" , "home on wheels" , "Extract for advance publicity" .)