Floor rust

[70 c10 rook]

So I'm waiting for my fuel tank to arrive and start taking out the old rubber mat and this is the only rust I find on the truck is the best way to get rid of this grind it out or does someone have another way? I was just going to grind it it doesn't go thru the floor and it's a little thicker than just surface in a couple of spots. Also my fuel tank was seeping is there a good cleaner that will remove the stuff it's like a thick lacquer. Thanks for any help.