Have doubts about us parking in camp (7)
I believe the answer is:
suspect
'have doubts about' is the definition.
(I've seen this before)
'us parking in camp' is the wordplay.
'parking' becomes 'p'.
'in' is an insertion indicator.
'camp' becomes 'sect' (sect is a kind of camp).
'us'+'p'='usp'
'usp' going into 'sect' is 'SUSPECT'.
(Other definitions for suspect that I've seen before include "One believed to have committed a crime" , "Have reason to believe" , "Person being accused" , "Have qualms about" , "Imagine to be true" .)