I know of a few guys that are off the grid. They were boren at home, never applied for a Social Security card. Work only on a cash basis.
When I lived in Anchorage, we knew an IRS Investigator, she had been trying to do an audit on this guy for years. She knew him, and saw him almost daily. He drove a 1953 GMC Bus that had been covered with wood paneling. That was his home, he moved it daily. That was the only record of his existance, he had registered the Bus so he could drive it on the road. The investigator had him picked up by the police one day. They took him to her office. She asked him questions, he just sat there refusing to speak. After about 10 minutes she was getting frustrated, he looked her in the face and said, "I don't exist, and you can't do anything about it". He got up and walked out. She became so frustrated with this case, she quit the IRS.