I lived in a van for a summer. I have a story, but I don't think it involves mental illness or laziness or wasting my life. I was working fulltime as a sysadmin at an Ivey League school and taking classes fulltime there at the same time. Yes, that meant I slept very little and had no "free time", whatever that is. One spring I was moving out of an apt I had rented with some friends for the school year and I had another apt set up for fall, but hadn't set up anything for the summer. My parents unmarked white utility van fit my bed perfectly and I decided to just not move my bed out and live in the van for the summer. I had a place to shower at work, I decorated the inside of the van, and it became home. I wasn't a creep, I wasn't homeless, my parents lived 45 minutes away so I had a fallback if it didn't work out, I had a place to shower, I had a job.
However, what I underestimated was how much people freak out if you're doing something even slightly outside of their concept of normal. I had found a great parking spot pretty near work, in a corner under some trees, however, within a week a construction worker called Safety and Security and reported a suspicious van (he was driving a jacked up mufflerless pickup truck with a rifle in the back -- who's the suspicious one?). 6am one morning, I was jolted awake by the loudest scariest banging noise I've ever heard, it felt like someone was punching me in the heart. A security guard was knocking on the sides of the van trying to see if someone was inside. I was too groggy/freaked to just stay put behind my curtains and tinted windows, I got out. He told me I can't sleep on college property, recorded my license plate and said they would be watching me.
I can't describe the lack of feeling of safety that having a locked door and a wall, specifically something thick that muffles knocking gives. I then tried parking on the streets discretely but had a hard time sleeping because I kept waiting for the cops to come knocking. I started parking a few miles away at a Walmart -- what a weird experience that was. RV's would come in and set up in a circle in the middle of the lot (I stayed on the outskirts). Every night around 2am some locals would come by and drive in circles around the RVers and throw bottles at them while yelling and squealing tires. No peace of mind there. I started parking at the local truck stop, no locals there, but now I had to worry about a sleepy truck driver backing into me in the middle of the night. Breakfast at the 24hr diner there was delicious though.
I started reading some forums about van living and found an article about how people who are forced to live in a car or van temporarily often find themselves pushed further into the fringes. I was doing this by choice, but I couldn't imagine someone who thought they could just live out of their car for a few weeks until their first paycheck from their new job could cover first/last/security deposit in a new city, only to be constantly hassled to move and then fired when someone at work found out. The numbers were troubling, something like 80% of people who temporarily attempt to live out of their cars end up actually homeless, jobless and carless.
Eventually some people renting an apt nearby and had a free parking spot let me park there. OP mentions loneliness. I didn't necessarily feel lonely, I was busy and had stuff to do, and I still had friends. But I definitely felt something, that people thought I was troubled, or needed help, or that something was wrong. And maybe they didn't really, but I realized that I myself was starting to avoid social contact. I would wake up early and sneak into work to take a shower before other people came in so they wouldn't notice, even though my boss knew I was living in a van and didn't care -- I wasn't going to lose my job if anybody found out.
When it came time to move out of the van, it was with mixed feelings. It as getting colder at night, and I would sleep better, but I had gotten used to it and now whenever I borrow my parents van to move something I feel nostalgic for that time when it was my home.
What I learned was that society does not take kindly to seemingly slight deviations from normal. The movie "Wendy and Lucy" came out a bit later and reminded me strongly of that outward push that society initiates on people who appear as "outliers". Certainly, it makes sense for the health of the system, but I was surprised by how tight the tolerances are.
I don't necessarily agree with some of the judgements you are making about how society treated you. You were acting strange and should not be surprised that people were concerned about you. There are also good social reasons why society doesn't make it easy for people to live in their cars. Safety, cleanliness, property rights, collection of taxes, etc.
You say "society does not take kindly to seemingly slight deviations from normal". I don't think your experiment that summer was a slight deviation. What you did was two standard deviations away from normal. If only 0.1% of society would ever do what you did voluntarily, that by definition makes it abnormal.
That's doesn't make it bad or wrong. Just not normal.
That's because it isn't efficient for society and people to not jump to conclusions. Nobody is going to take the time to see that your situation is really different then the creep that is living in a van parked outside a school for a different reason.
We hear plenty of stories of how Bill Gates and Jobs didn't shower and of course we know that they ended up fine. But we don't have any data to compare on people that followed the same strategy and didn't end up in a good place because society jumped to it's natural conclusions about people who eschew all social graces.