Unfortunately, since you need to get inside the frame to take the bumper off, I can't really weld them up. I'm thinking about just tacking some 1/8" plate over them, that I could quickly knock off with a hammer if I needed to remove or tighten the bumper bolts. I guess I could also make up some covers that are held in place by a couple of screws.
I am going to fab up a mini skid plate for the oil filter. I really don't like it hanging out there, like it is.