Camp male's maintaining apparel on the outside (6)
I believe the answer is:
stalag
'camp' is the definition.
(German prison camp in World War 2)
'male's maintaining apparel on the outside' is the wordplay.
'male' becomes 'stag' (a stag is a male deer).
'maintaining' is an insertion indicator.
'on the outside' means to remove the middle letters.
'apparel' with its middle taken out is 'al'.
'stag' placed around 'al' is 'STALAG'.
(Other definitions for stalag that I've seen before include "German prison camp in WW2" , "Type of German prison camp" , "WWII German prisoner of war camp" , "German POW camp in WWII" , "German prison_camp" .)