Because I don't want to pay property taxes in the long run or be stuck in a bad situation.
My own personal situation makes it nearly unfeasible for me, as a single person who is socially isolated and displaced and the lowest one can possibly be in the social strata, it is far too risky and not a wise decision for me to buy property and develop it. Unless I lived in a proper community of people and have a family going on for me.
Yes you are exactly right about the "legal issues" since it's a grey area, and the Cabin or Tiny House has different zoning / legal definition terms in all sorts of different areas. So I am looking for a place where either it can be done legally or even if under the radar.
Unless I find some other arrangement where somebody already has a cabin that I can rent out very low or offer caretaking or some other service, like if they live on a farm. There is a high likelihood that most people in the future are not going to be able to earn enough income to even pay their property taxes at the rate things are going.
If I have the portable cabin / house, I don't plan on developing anything on the land, unless it was somehow in mutual interest for the long-term with the property owner to do that, but at most I would have a makeshift patio and other means to manage septic challenges rather than having one built.
You'd be paying property taxes on the structure.... Non-primary structures are taxed just as much as houses, it's based on square footage usually.
They'll send a drone or drive-by assessor and your landlord will get a tax bill most assuredly.
So your lease price will include that property tax or they'll ask you to pay this separately.
You'd need to title it as personal property, to retain ownerhsihp, but you'll still be taxed on it.
I understand what you said and myself been in and out of this kind of situation plenty, but you'll still have to develop the land to live on it. You won't be able to hook into someone else's septic, the septic rules are crazy strict everywhere except Alaska now, and they do enforce. Neighbors call and report this stuff all the time, also. You'll need to develop access driveway, clear/level the pad, pour concrete, install septic, run trenches and lay piles and wires, all this costs a lot, and you'd waste time investing into someone else's property, losing these money.
If someone has a ready installed RV pad, with concrete, electric, water, and sewer connection, that's the only situation there it could make sense, but again, it's illegal to permanently live in temporary structures almost anywhere and this does get reported, so you'd expect to be asked to leave any moment - you don't want to be stuck in signed long-term land lease in this situation. If you're set on living in temp structure, you can least could develop your own land with pad and then sell it if you have to leave, at least you'd keep invested money or even make money on this. Land with ready pad is easy to sell. It's hard to get out of bad/failed lease, much easier to sell developed land now.
In many states, rural property taxes are very low and wouldn't be an issue.
There're few remaining rural areas out there where people don't get hassled by the county over living in temporary structures... Some also build "workshops" and live in them secretly, to circumvent septic rules (but still best to do it on own land, not to lose money invested in the improvements). There're places where you can do a septic cheap for 3K, though.