Advertisement for American's caravan (7)
I believe the answer is:
trailer
This clue is a double definition.
'advertisement' is the first definition.
(I've seen this before)
'american's caravan' is the second definition.
(US term for a caravan)
'for' acts as a link.
(Other definitions for trailer that I've seen before include "Mobile home; preview" , "[(type of) PARK]" , "Vehicle hauled by car or truck" , "ground plant" , "Short scenes from a future film" .)