Yes, Stock tank, foam all around. I had a piece between the tank and the wing that held it in place when the wing was mounted. I had never had one come loose on the bung either. It surprised me! It must have been working it's way loose for a long time and finally got real loose as the screw was several threads from even beginning to tighten. I have this same bung setup in several of my other planes. I plan to check them all and rtv them so they can't back out.
I've never had one of the sullivan plastic bung plates loosen on me.
Later,,, basmntdweller