Suggestions needed: Repairing a cut hole in floor (rear)

[Green Monster]

It's time to replace the decade old carpet in Green Monster and while the carpet is up I'd like to repair the hole in the floor by a previous owner. The hole leads to access the top of the poly gas tank so I'm assuming the hole put there for easy access a fuel level float sensor on the original tank.

Regardless of the reason, I need a little help on the best way to patch the approximate 5" diameter hole hole.

I was thinking of getting a 7"x7" square of corrugated bed material then using adhesive to seal it. The trouble with bed material is it comes in 16"x48" lengths- way more than I need plush shipping is expensive for an over sized item. And I've read on this forum of members who purchased patch panels don't match the existing floor rib pattern.

Is there a better method to correct this? I'm open to suggestions.

See photo of hole in floor below.