Care of a large ship involves months for worker down below (4,5)

I believe the answer is:
coal miner
'worker down below' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.
'care of a large ship involves months' is the wordplay.
'care of' becomes 'co' (c/o can mean 'care of' when addressing mail).
'large ship' becomes 'liner' (I've seen this in another clue).
'involves' is an insertion indicator.
'months' becomes 'm'.
'liner' going around 'm' is 'lminer'.
'co'+'a'+'lminer'='COAL-MINER'
'for' acts as a link.
Can you help me to learn more?
(Other definitions for coal miner that I've seen before include "Digger" , "person working mostly in the dark" , "No miracle (anag) - endangered species?" , "I'm dirty when I'm working" .)
