It has wheels. Do you have any plans to move this thing? EVER? Because trailers flex, and there are two strategies for dealing with that.
#1 make careful material choices so the trailer structure can flex without taking damage. That's where drywall and mud may not be your best choice, for instance.
#2 make the trailer base and structure, so rigid and strong that it forces all the flex into the suspension. You might think #2 happens automatically, but it does not. Either way, you have to deal with the forces at hand.
The reason for thin walls is simple: it adds square footage. If motion is an issue, I'd say "think like an airplane not a house". Airplanes are insulated.
Unfortunately, the simple-living and alternative-energy communities are often hijacked by the "I wanna live in squalor", "gov't off my lawn" and "off-grid, like the unabomber" fringes. Look at any of the "government shutting down timy-homes/off-grid tech" and it's actually the latter they're concerned with: drinking downspout-water or not having smoke detectors in a house full of kerosene heaters, which is usually about being "cheap, the bad way".
And in your town, you will be one of the people swaying the government on the question of whether tiny-houses are good or bad. My advice is be a good ambassador: don't be cheap, be classy. Be the magazine showpiece tiny home, which is done less in dollars than in time, care and pride. (well old-pride, when it was a motivator to excellence, not new-pride, which is puffery instead of work.)