I know of two situations where people were living on small pieces of scrap woods back when I was growing up in Delaware County. The one guy got arrested because he tried to rape someone.
The other one was living in a homemade shack in woods that had a creek on one side and a highway on the other. I used to walk the woods in search of antler sheds and I came upon his shack. It was an eerie feeling because there was a clothes line with clothes on it, a fire smoldering and other belongings around including a pot with water in it. There were also tons of empty shotshells around. It was apparent someone was living there and this was within 10 miles of Philadelphia. I got out of there and stayed away because I felt like I was being watched and it might have been a nut.
I think you could get away with it for a good while if you kept a low profile. Remember the Olympic bomber who lived for years on the national forest land in North Carolina. He was out there for several years despite the FBI searching for him.
Big tent set up out on Michaux a few years back. Not just hikers passing through. Had a 'permanent' dwelling set up there just off the AT. Yep, agree with the eerie feeling when you come upon that kind of thing.
There are quite a few homeless people. And that's what we're talking about here. They aren't doing some kind of adventure project. They've got no place to hang their hat, no housing, so they're outdoors, trying to survive.
There was a guy sleeping in a little tent along Spring Creek in Bellefonte. A lot of people knew him and knew he was out there. We had a cold snap this past winter and he was found dead in his tent. Died of exposure according to the authorities.