Do we? I don't think we do anything cheaper than an SRO. At the very least, tents in public areas (or on private land!) are not the answer. In any case, we have these campground solutions already. They are called "campgrounds". They are just not an efficient use of urban land, although sometimes they also exist close to cities, e.g. some in Hawaii iirc.
Mainly though, this is a strawman. Tents themselves are not the biggest problem when they don't e.g. block a sidewalk, piece of public infrastructure, or a road. The problem is piles of garbage, needles, dumping sewage into lakes and streams, increase in crime, not-yet-criminal or never-prosecuted safety concerns (e.g. someone I know can no longer take an obvious bike trail to where they're going because of some close calls with aggressive barely human campers).
What I had in mind is that we need to solve those accompanying problems in order to make living in tents socially acceptable.
Tents show up on public areas and sidewalks because there are no better established places for them.
Trash accumulates around tents because there is no established garbage collection procedure like there is for buildings.
Maybe the solution is some kind of campground with a low fee.