Interesting thread!
I really miss my A frame right on the river, I could sit on the deck and flip a penny in the water less than twenty feet away. There was a large barn on the property for storage and it was a weekender just outside of town. Laid out pretty much as described above. Sold it a got a cabin at the lake, it's just under 1000 sq ft not counting a long sunroom addition and I lived in it for a few years. I found I only use the livingroom with a hide-a-bed couch, a small kitchen and bathroom, about 500 sq ft! The LV was 14x24 and with a wall of windows facing the water so it seemed huge in a way. All of this to say that while we get use to larger dwellings, you really don't actually use much space at all.
Tiny houses, on a trailer are unique. I think they can work well for some people, especially moving to financial freedom. IMO, they should be totally off the grid capable, a good battery bank and solar aray maybe wind as a backup, much like sailors employ.
I'm surprised no one mentioned "Park homes" smaller house trailer/mobile homes, manufactured small homes. I looked at one, they were asking 80K and rented the lot! That just doesn't cut it to me, you can buy a real home for that.
Financially, I believe utility bills will exceed many house payments, take a ranch style 1800 sq ft, with current rates you can have a payment under $400 easily. I'll bet in another 10 years it will cost $400 in this area for utilities on a 1800 sq ft home conventionally built. So, off the grid would be great, having a smaller foot print and cost to live.
As to which one, an RV or TH, whatever trips your trigger. Here, either one would be taxed as personal property, anything that is used as a living space can be considered a mobile home, wheels or not. Lowe's sells a small storage building where one is tricked out as a cabin.
Sorry, I'm rambling, I got up too early!