This add-on is almost the same as google-base only you dont need to do anything
Just upload this extension and go to yourstore.url/index.php?route=extension/feed/feed
and you'll see the xml

in google merchant use this url to create product feed and google does the rest
here is a demo link
https://demoshop.cc-b.nl/index.php?route=extension/feed/feed

the extension will be upgraded soon with extra features to set for google so for now this simple extension will be free

if you sell adult good or used good message me and ill explain how to set those variables

only tested at version 3.0.3.2 but i guess wil work on all 3x versions

installation:
just go to the installer in extensions upload the ocmod and refresh in modifications

Side note on Valuta!!!!!
The extension is made with the base valuta so
*dollar
*pound
*euro

in the source you can add your valuta when you get a error on price