I know others may not agree with this, but if the kitty is fine with living out of the box, I don't see any reason to put him in a kill shelter when he has a perfectly good temporary home right there. It seems you live in a somewhat rural area where high traffic areas aren't too much of a problem so I say keep him right there until you find a home for him.

He's adorable, sure does look like a friendly sort. Have you checked with neighbors to make sure no one is looking for him?

Good luck and let us know what you decide to do.