Quote Originally Posted by buildingblocks View Post
I can say that my provided isbn numbers shows up in the gtin field in my google merchant account when viewing a product containing an isbn. You may find that your upc number also falls in the gtin field.
Think I've finally got it going, more or less. My default Google Product Category isn't going into the XML but I don't think any of my products *have* to have it so no great loss.

Thanks for the help everyone, much appreciated.