The "tiny house" movement is alive and well in places like Portland, OR, and on the Home and Garden TV cable channel. Supposedly, anything less than the 500 square feet qualifies. And you see articles like this one from Canada's Globe and Mail, about people trying the lifestyle and giving it up.
This whole thing leaves the DrsC somewhat bemused. We have owned RVs for over 43 years and have lived in them for several months at a time. In fact, as I write this we are 30 days into an RV outing planned to last 75 days.
Our current (and largest) RV, when fully "popped out," has about 348 square feet. Only some of that 348 is floor space, the queen bed, counters, cabinets, closets and refrigerator all take up room, as do a dinette and chairs, sofa, and two recliners. We qualify as a "tiny house," any RV does.
Even more like a "tiny house" are the so-called "park model" RVs that are meant to be used exactly as HGTV's tiny houses are used. That is, towed to a site, connected to utilities, and lived in.
What we don't "get" is why people are reinventing this particular "wheel." It already exists and you can go see park models on an RV lot if they're legal in your area.
If park models aren't legal in your state, any RV is effectively a tiny house and RV parks provide places to site them, paying rent of course. RVs aren't insulated to blizzard standards so parking in a relatively warm climate makes sense in winter.
Lots of people "full time" in RVs for multiple years. We've known several couples who've sold their homes to go wandering and loved it.