We've been building tiny houses for the past year and a half (4 houses total, two of which we've sold). After talking to a couple of hundred people interested in tiny houses, here's what we've learned:

The wheels/trailers are "dumb" because almost nobody wants to move them once they get them in place. So as far as we can tell the only reason to build on a trailer is to avoid regulations in many locations throughout the US (an example: where we are in New Mexico if you build a house on a foundation you need to hire licensed plumbers and electricians whereas if you build on a trailer you can DIY; needless to say licensed professionals are far more expensive that doing it yourself so there are significant savings when you DIY).

The people interested in tiny houses seem to fall into three buckets (maybe 4): 1. people who want an Airbnb on their existing property (these are usually well-to-do folks who don't bat an eye at the pricing) 2. older folks who don't have the means to retire in a normal-sized house 3. younger folks who don't have the means to live in a normal house 4. if there's a 4th, it's younger folks who want a vacation house that they can Airbnb when they're not using it.

These 4 markets seem quite large based on the number of people who have reached out to us when we do pretty minimal marketing. And the reason we started doing this in the first place was to build below-market-rate housing (i.e., targeting groups 2 and 3 above), but there's a bit of a paradox going on here that we're trying to solve: groups 2 and 3 do not have the means to buy houses (tiny or not) outright so the only way we're going to crack this nut is if you can finance the purchase. We think we've found a way to do that, at least in our local market of Northern New Mexico, and we're just going through the proper channels with our local county to test this concept because lenders of course require that what you're building is legitimate. We're still hopeful that this will be a good solution locally, if not more broadly. Btw, we have never given a thought to trying to do this in an urban area. Doesn't seem sensible given land values where cheaper housing is almost by definition multifamily (i.e., >=2 units on a lot).

Edit: Oh, duh, here's a link to the house we build: https://santafe.craigslist.org/reo/d/el-prado-brand-new-full...