Possibly that small, but I'm a family of five so sleeping that many quickly becomes a problem. Bunk beds and squeezing in are fine but we're +1 over what almost every dwelling considers family-sized.

I hadn't considered a trailer because that usually requires a commitment to owning a huge truck. But are these trailers you are referring to more semi-permanent?

Yeah, agreed, I've had so many conversations about this where people like the idea in concept but when you hear about people actually living in these it quickly becomes clear that it doesn't work for some folks. Specifically, though, in the 400 SF version that we'd like to build next (assuming we're able to actually sell the smaller one we're currently building) it would be on a 30-foot trailer and actually have two sleeping lofts. In that model, a minimalist family of 4 (minimalist, he says, as if!) could totally fit with the two adults in one loft and the two kids in another. At 3 children you start getting more difficult, but I'm sure you could do a 600 SF house, but then a trailer large enough to build such a thing becomes difficult to move.

Re needing a truck, plenty of folks tow tiny houses so that's no problem assuming you don't want to constantly move it. If you wanted to be truly mobile I personally question whether a tiny house really is the right vehicle (ha!) for that lifestyle. And the trailer we're using has jacks, which stabilize the trailer so, no, it's not semi-permanent, but when you jump around in ours you can't feel it moving at all. We also had a thought about adding a skirt to the trailer itself to increase curb appeal if someone purchasing it is going to leave it fixed in one location, but that's for when/if we sell. Gotta finish the interior first.

Semi-permanent trailers are common. Most camper trailers are not designed to go cross country - they are for the family who does a couple in-state vacations every summer. (at the cost of fuel a mini-van + hotel room is the same price as a truck + camper if you drive for 10 hours every day - that is assuming you have the truck and camper anyway and so there is zero cost to buying it)

See: Destination Trailers

https://www.forestriverinc.com/rvs/destination-trailers/sier...

Using a trailer is the technique to bypass council judgements in Australia as well. Here are some Airbnb examples:

https://cabn.life/book-now-2/

Some of these would cost AU$70-110k though.

It depends on the State, but in most parts of Oz, you need a Building Permit, then a Certificate of Occupancy to be able to live there.

The exception appears to be where there is already an approved dwelling on the land, and even then a Caravan can only be used temporarily (eg in your example of temporary AirBNB accommodation).

I know because I've just lost exactly this battle with the local council.