I'm not sure what the purpose of the knockouts is but you don't need to remove any to remove the skid plates. They don't cover any bolts. I was actually told by a rust check guy to remove them. The skid plates hold a lot of moisture and rust the undercarriage. Removing them gets more airflow to dry it out. I've got to admit there seems to be a lot more rust on mine where the skid plate is. Just a thought.