Vessel preferably parked outside church (8)
I believe the answer is:
schooner
'vessel' is the definition.
(type of ship)
'preferably parked outside church' is the wordplay.
'preferably' becomes 'sooner' (eg 'I'd sooner sit' means 'I would prefer to sit').
'parked outside' means one lot of letters goes inside another.
'church' becomes 'ch' (common abbreviation).
'sooner' enclosing 'ch' is 'SCHOONER'.
(Other definitions for schooner that I've seen before include "boat" , "Type of glass" , "that carries sherry" , "Item used for drinking" , "Sailing vessel used in former times" .)