Piccolo occasionally kept inside box in this compartment (7)
I believe the answer is:
cubicle
'this compartment' is the definition.
(I've seen this before)
'piccolo occasionally kept inside box' is the wordplay.
'occasionally' indicates alternate letters (letters taken at regular intervals or occasions).
'kept inside' is an insertion indicator.
'box' becomes 'cube' (boxes are cube-shaped).
The alternating letters of 'piccolo' are 'icl'.
'icl' put inside 'cube' is 'CUBICLE'.
'in' is the link.
(Other definitions for cubicle that I've seen before include "bay" , "Booth - kiosk" , "Small room for special use" , "Small changing room" , "Partitioned-off part of room" .)