Thank you!
I'm a ceramist. I threw a large, low vessel with stoneware. When it was firm enough to handle, I cut it and lined it up with a template I had drawn. Single fire for both bisque and glaze because I'm impatient. I used silicone adhesive to hold it in place, let it cure (MUST BE PATIENT), and then filled on either side.
I would absolutely recommend this method!
Were I to do it again, I would use the adhesive on the sides as well as the bottom and would fill less. The place where the substrate is higher than the edge has minor landslides occasionally.
You want to use a clay and glaze that are food safe. I don't know what your access to clay and kiln looks like. There are often open studios at community colleges and sometimes in malls.
I'm on my phone, so I can't see your whole profile. Is this the 45 gallon?
I did make two of these borders. The one I didn't use is lighter and more smooth. It's two pieces. Would you be interested in it?