1000kg gold for car cover (7)
I believe the answer is:
tonneau
'car cover' is the definition.
(I've seen this before)
'1000kg gold' is the wordplay.
'1000kg' becomes 'tonne' (a tonne or metric ton is 1000 kilograms).
'gold' becomes 'Au' (Au is the chemical symbol for gold).
'tonne'+'au'='TONNEAU'
'for' is the link.
(Other definitions for tonneau that I've seen before include "Open-top car cover" , "car's back seat" , "Protective cover for open car" , "vintage car part" , "Part of open car behind front seats" .)