I'm not nuts about the cover letter; the pamphlet speaks for itself.
However you do it, keep a record of the fact you did so. If you file a SAR on the customer for structuring note the distribution dates for the pamphlet in the narrative. LEAs love the idea that the customer cannot say 1) he did not know what structuring was and 2) he did not know it was illegal.
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In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.