Why the steel wool? Doesn't that rust away rather quick?

I would just patch it up with concrete mix worse case. Knock/brush out any loose material before patching it up.

Tomorrow at work I have to use two pop rivets to finish up the screen on the air vent and it's done. That vent airs into the porch that was also turned into a room long before we purchased this house. It's also been a couple of weeks and I haven't caught any more rats. I'll pull the traps and assume all is clear now.