Looking for a script which will add a prospect to a specific campaign based on a field in the prospect card.

Essentially, we have a field in our prospect layout called "Renewal Month" which is populated with the months of the year.  I have a campaign set up for each month so I can run email marketing for each month based on a renewal timeline.  So there we have 12 campaigns called January Renewals, February Renewals and so on.

What I'm looking to do is have a prospect added to the campaign that is specific to their renewal month listed in their prospecting module.  This way, if a prospect is added or updated with a different renewal month, it will place them into the correct campaign.

I looked at the GetRelated and UpdateRelated and couldn't really tell how to make this happen.

Any thoughts on this?