Shares with awfully sick miners, backing shelters (5,2)

'miners backing shelters' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'shares with awfully sick' is the wordplay.
'shares' becomes 'mun' (I can't explain this - if you can you should believe this answer much more).
'with' is an insertion indicator.
'awfully' indicates anagramming the letters.
'sick' with letters rearranged gives 'cksi'.
'mun' enclosing 'cksi' is 'MUCKS IN'.

Can you help me to learn more?