My beef about park models is usually the lack of beef in their insulation, usually R11 or lower wall insulation. This manufacturer, GreenFLEX, (click on link for more photos or to download brochure) in Salem, Oregon, makes environmentally friendly park models with concrete SIPs (Structural Insulated Panels) that are R16.
The manufacturer also has a note in their downloadable brochure claiming that R21 insulation, which would be very good on some 2x6" conventional framing, performs in the real world at R13. SIPs, with their solid-core foam insulation, probably do function better in the real world than fiberglass with conventional framing. I'll go along with that.
Their floors are R22 and ceilings, R30, which is good, especially for a park model.
The ceilings are 8' high, which is good height for a small home. I also like their simple design. It doesn't make you go squishy inside because it's so cute, but just being small makes it cute, and the interior looks nicely planned and simple.
These are also meant to be reasonably priced, including a more stripped down kitchen for worker housing, or if you want, a more upscale kitchen. The website doesn't mention prices.
It comes in a flat roof model and peaked roof. I'd go with the peaked roof. Here are some photos. In the first photo I GIMPed in some foundation/steps: