Two vehicles around a trailer (7)
I believe the answer is:
caravan
'trailer' is the definition.
(caravan is a kind of trailer)
'two vehicles around a' is the wordplay.
'two vehicles' can mean two replacements for 'vehicle'.
'vehicle' becomes 'car' (car is a kind of vehicle).
'vehicle' becomes 'van' (van is a kind of vehicle).
'around' means one lot of letters goes inside another.
'car'+'van'='carvan'
'carvan' placed around 'a' is 'CARAVAN'.
(Other definitions for caravan that I've seen before include "Towable home" , "Group of desert voyagers" , "Towed accommodation" , "Group crossing a desert" , "Camel train" .)