I've neglected to respond to anonymous loud knocking that may or may not have been police.
The one time I have been woken by police, it was outside my area and the first night I'd ever spent in the minivan, so I was incredibly disorganized and drowsy. I tell them the truth--I'm in here because I live in a van. They took it in stride and didn't give me grief over it, didn't even ask me to move....just said that "technically" I wasn't supposed to park there overnight and asked when I planned to move along since nearby businesses would be opening soon and need the parking space. (It was right frickin' down the street from where I lived for10 years and it's used as extra parking by the locals all the time. If only some idiot hadn't been disturbing the peace nearby no one ever would have noticed my van.)
If I ever need to soften the "full time" aspect of it, I have documentation and external indicators that I'm chronically ill, and I can excuse my setup based on "I need to lay down and rest often, this setup helps me travel to medical appointments and live more independently". Even if I had housing, I'd still need my van and setup anyway, so passing it off under medical reasons is legit.