Complain boat is where vehicles should be (3,4)
I believe the answer is:
car park
'where vehicles should be' is the definition.
The answer is a location as well as being a singular noun. This is suggested by the definition.
'complain boat' is the wordplay.
'complain' becomes 'carp' (carp can informally mean to complain or whinge).
'boat' becomes 'ark' (ark is a kind of boat).
'carp'+'ark'='CAR PARK'
'is' is the link.
Can you help me to learn more?
(Other definitions for car park that I've seen before include "Multi-storey building with bays" , "multistorey, for example - with 27d" , "place with many bays" , "of which many stories might be told" , "Place to leave vehicles" .)