Towed vehicle (7)
'towed vehicle' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for caravan that I've seen before include "Mobile home" , "Towed accommodation" , "Group crossing a desert" , "Holiday vehicle" , "Home on wheels" .)
(Other definitions for trailer that I've seen before include "Short film advertising programme" , "Short film advertising a forthcoming feature" , "Forthcoming film ad" , "TV ad" , "Vehicle hauled by car or truck" .)