Vehicle with heavyweight container (6)
I believe the answer is:
carton
'container' is the definition.
(carton is a kind of container)
'vehicle with heavyweight' is the wordplay.
'vehicle' becomes 'car' (car is a kind of vehicle).
'with' says to put letters next to each other.
'heavyweight' becomes 'ton' (a ton weighs a lot).
'car'+'ton'='CARTON'
(Other definitions for carton that I've seen before include "Sydney -, Tale of Two Cities hero" , "A cardboard container as for milk" , "Box made of cardboard" , "Container for food or liquid" , "fictional lawyer" .)