Sailor man in canvas cover (9)
I believe the answer is:
tarpaulin
'canvas cover' is the definition.
'tarpaulin' can be an answer for 'cover' (I have seen 'protective cover' mean 'tarpaulin' so perhaps 'cover' could also mean 'tarpaulin'). I also know that 'canvas' relates to this answer.
'sailor man in' is the wordplay.
'sailor' becomes 'tar' (slang term for a sailor).
'man' becomes 'paul' ().
'tar'+'paul'+'in'='TARPAULIN'
(Other definitions for tarpaulin that I've seen before include "It provides protection" , "seaman rarely required" , "[SHHET]" , "protective headgear" , "Strong waterproof sheet" .)