We have a couple in our city that have a white panel van (no windows other than the back door and they are covered by Reflex material), a roof rack (that is either mostly empty or has some small gas cans on it) and they have been camping / boondocking for 3 years now. I will see them in a city park during the day, or Walmart parking lot at night, or on a side street.
I have pointed them out a number of times to my wife as she always misses them, even when parked a few spaces away.
Some days a lady will be sitting in the front seat reading a book but most times it is just another empty vehicle.
Honestly I think most common people/ people of authority will just leave a vehicle like this alone.
I have seen a couple truck campers around my house and a class a that just pulled into the ice rink parking lot and camped / boondocked in the corner. Most people would not even notice them, even walking by a few feet away. Plus unless you were in charge of a place like that you have no idea if they are suppose to be there or not.
Only issue I see is in a resort area. I have been told by a few people that they could not even park on a road during the day in some resorts without getting harassed and told to go to a campsite and I understand this.