'65 Barracuda Trunk Floor Doubt (question)

I have a picture of the trunk floor before having removed the large, black sheet metal plate which shows the corner gap underneath the filler pipe being filled in by "something". I can't tell in my old photo what actually is covering up that space (and three years later can't remember for the life of me). Thank you.

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trunk corner 1.JPG

trunk corner 2.JPG