Hi Kevin,
I work at Bigcommerce. I can definitely help you set this up. In order to get your blog running as a subdomain. You will just need to create a 301 redirect within your control panel.
The first step will be to select the Website Content tab in your control panel, and then select Create a Webpage. Next to “This Page Will,” select Link to another website or document. Fill in your page name. This will be the name of your link.
Then, you will want to go to Tools–> DNS Records to finalize the redirect.
Ex: Host: blog.yourstoredomain.com.
Type: CNAME
Redirects To: yourblogname.com
Here’s a great support article that outlines all these steps with screen grabs. https://support.bigcommerce.com/questions/1181
In addition, if you have any questions or issues, please feel free to contact me anytime. Or, you can submit a support ticket or give us a call. We’ll be happy to help you get this working.
-Jessica
