Hi Steve

What Storefront version are you running? If your SKU is already displaying on the page, it may already be picked up by Google.

Furthermore, the Storefront also emits structured data for Google. If you look the HTML rendered source of your product detail page, you'll find a section near the text that should print your product data including the SKU.

<!-- SEO structured data -->
<script type="application/ld+json">
....
...
</script>

You can use this testing tool to enter your page URL to see what structured data is picked up by Google.

I hope this helps.