XML Resource: https://support.google.com/merchants/answer/7052112?hl=en

First, the settings: (ignore the "scotty" and uri access thing, that was for testing on the site I screencapped this image from)

The feed template:

Settings:

Templates: Be sure to update custom information below such as store name, description, image links, etc

Details template:

<mvt:item name="templatefeed" />

Header Template:

<?xml version="1.0"?>
<rss xmlns:g="http://base.google.com/ns/1.0" version="2.0">
<channel>
<title>Store Name goes Here</title>
<link>Link to store goes here</link>
<description>Store description goes here</description>

Iterator (loop) template: See custom field example in this loop (brand). The custom field must be selected in the miva merchant awesome 1990's custom field boxes.

Images: Use scots tools to find the id of the "main" image type (or whatever they are using) and put it in the ProductImage_Load_Type function.

<mvt:assign name="l.settings:productimage" value="''" />
<mvt:assign name="l.settings:image" value="''" />
<mvt:do file="g.module_library_db" value="ProductImage_Load_Type(l.settings:record:id,1,l.settings:productimage )" />
<mvt:do file="g.module_library_db" value="image_load_id(l.settings:productimage:image_id,l.settings:image )" />
<item>
<g:id>&mvt:record:code;</g:id>
<g:title>&mvte:record:name;</g:title>
<g:description>&mvte:record:descrip;</g:description>
<g:link>&mvt:record:canonical_uri;</g:link>
<mvt:if expr="l.settings:image:image">
<g:image_link>&mvte:global:secure_baseurl;&mvt:image:image;</g:image_link>
</mvt:if>
<g:condition>new</g:condition>
<g:availability>in stock</g:availability>
<g:price>&mvt:record:price; USD</g:price>
<g:shipping_weight>&mvt:record:weight; lbs</g:shipping_weight>
<mvt:comment>
<g:shipping>
<g:country>US</g:country>
<g:service>Standard</g:service>
<g:price> USD</g:price>
</g:shipping>
</mvt:comment>
<mvt:if expr="l.settings:record:customfield_values:customfields:brand">
<g:brand>&mvte:record:customfield_values:customfields:brand;</g:brand>
</mvt:if>
<mvt:if expr="l.settins:record:sku">
<g:sku>&mvt:record:sku;</g:sku>
</mvt:if>
</item>

Footer template:

</channel>
</rss>