How to edit Google data feed to add brand and shipping weight?

Hi I'm using Zen Cart 1.3.9h and I have the Google Merchant Center Feeder add-on installed. it works perfectly and sends the data feed.
But now Google is telling me I need to add brand and shipping weight.
I have an xml file and I'm not sure how to edit it, especially with 163 items.
Is there any way i can add all this through zen cart?

It should add the brands unless expressly configured not to in the admin options. In each product definition have you selected a manufacturer?

Show Weight is an option in the admin.

torvista:

It should add the brands unless expressly configured not to in the admin options. In each product definition have you selected a manufacturer?

Show Weight is an option in the admin.

I checked all of my products, they all show manufacturer and weight. But for some reason Google Merchant Center still tells me the shipping weight is missing :S

Can you please be a bit more detailed? Sorry I'm really new to all this.