Add fields to Sales Invoice form - Is VBA Modifier the solution?

Hi.  We have a request to be able to track a second quantity and Unit of Measure on an Invoice Line.  This information comes from another system, and we eventually want to import from that system into GP using an integration (eConnect).

For example we sell a product by weight, but also want to track number of packages. There is no equivalency setup, because 10 Packages could be 500 KG or 525 KG or 499 KG.  We just want to be able to track both for reporting purposes.

Is VBA Modifier the solution for this or are there other ways we can do this?

With VBA Modifier can we actually create fields in GP tables? I don't know how this works.