Trailer (7)
'trailer' is the definition.
(caravan is a kind of trailer)
This is the entire clue.
(Other definitions for caravan that I've seen before include "Motor-home" , "Towed home" , "Group crossing a desert" , "Camel train" , "House on wheels" .)
(Other definitions for tracker that I've seen before include "follower" , "One can follow" , "Rod in organ mechanism, trailer" , "fund" , "Investment" .)