I ended up generating the correct gltf file url when I inject my app bundle and storing the app URL in a global store at the app root.
Also made sure to copy my gltf file to my dist so that the bundle has it for reference in prod AND ensure this file is a web_accessible_resource in the manifest.
A virtual pet floating around on my page as an addon. 
Full video: https://i.gyazo.com/f2346da98006a1238f254273b9c5accd.mp4
