I'm not sure if sequence-xxx variables available in this way (in a method, called inside of a loop). Maybe it will work in this way (see lines inside your quoting). Warning: untested
<!-- meth_step_2 (I think this is ok - but I guess that this is where the problem lies) --> <!--#with sql --> <!--#in marketinglist -->
<dtml-call "REQUEST.set('my_item', _['sequence-item'])">
<!--#call insert_holding_table --> <!--#/in --> <!--#/with -->
When I display <!--#var sequence-item --> within the in statement, the correct values display, they're just not seeming to make it to my query.
<!-- insert_holding_table (this works by itself, but perhaps not when called by a dtml method) --> insert into mHoldingTable ( dealer_code ) values (
<dtml-sqlvar my_item type="string" >
);