Quantity Business Processes

 Has anyone worked with Quantity type BP's. For instance we want to track how much product we have. So we have a Quantity BP, Quantity Change, and a Quantity Used BP. Quantity BP is the initial amount, Quantity change will add quantities when ordered and Quantity Used will be a daily/weekly/monthly entry of how much of the product was used.  The catch is we have over 400 products so we want to use line items to keep the number of records down. We tried using QBDE but they are not allowed on Line Items. The QBDE's would have take the