Margi cracking up The Hill with seasonal traveller (8)

I believe the answer is:

migrator

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'seasonal traveller' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.

'margi cracking up the hill' is the wordplay.
'cracking' indicates anagramming the letters.
'up the hill' becomes 'tor' (I can't explain this - if you can you should give a lot more credence to this answer).
'margi' anagrammed gives 'migra'.
'migra'+'tor'='MIGRATOR'

'with' acts as a link.

Can you help me to learn more?

I've seen this clue in the Irish Times and the Irish Times (Crosaire).

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