At least in California, there are a lot of public support programs. I mean, a looooot of public support programs. A LOT. Like, to the point where the state is spending tens of thousands of dollars for each homeless person, and probably north of $100k per person per year for a subset. Talk to a firefighter or paramedic in a CA city sometime. They will tell you, there's "regulars" that they have to deal with every single week. The cops and firefighters know all of them by name.

We're paying hours a day in overtime to basically have the cops, firefighters, and EMTs deal with the same small population of mentally ill people on the same street corner every week, for years. These people cannot get better because they choose not to stay in the mental hospital or substance abuse programs offered to them. Someone is 5150'd, placed on a 3-day hold, and 72 hours later they walk out of the hospital and back to the same street corner, where they have a mental breakdown again the following week. You can offer support -- they will basically tell you the same thing, I'm not sick at all, there's nothing wrong with me, I am not a danger to myself or others, and you are shit out of luck.

At the same time, there are way more homeless people who are silently and cleanly living in their cars and showing up to work every day at a low wage job. Most people won't ever see them unless they look closely. Visit /r/urbancarliving sometime to get an idea of what that population looks like. Those people might get a 15 minute "knock" from the cops once a month.

The actually progressive option is to involuntarily incarcerate people who need it, while not criminalizing car/RV living, offering work placement services, housing assistance etc. The most realistic thing would probably be to build subsidized mobile homes and clean, low-rent central places to park an RV.

You correctly identified the biggest thing here though which is making housing affordable. Unfortunately, that will never happen.