Hi There T E Mollerus,
Are you just looking to display the Warehouse/Site Info on the Line Items Grid for these transactions? These fields are actually already on the grid - Just Hidden. You can load up your Invoices/SO screen, and click on the small gear icon underneath the Line Item Grid - And check the Boxes for Location Site and Location Bin which will display the Warehouse info for these items.
You can make these fields display on the grid by default with some Simple Customization - Let me know if you want to pursue this option and we can go over this one together.
What would the final workflow look like for you? Is simply displaying this (editable) info on the LineItem grid acceptable? Or did you want to build out some kind of onscreen validation?
Regards,
Ben