This 'caravan' (UK English for trailer), from Retreat Homes can be parked almost anywhere, thanks to its wheels, but it's far from a trailer:
"Classified as a transportable building, it is ready to move into within days and can be situated in places that a conventional home cannot..."
Shedworking loved the idea:
"Although it's aimed at a holiday home market, there is a garden office option....with floor to ceiling windows, oak floors and kitchen or bathroom options, plus furniture suggestions."
company: Retreat Homes
style: modern trailer
size: 480 sf - 1,000 sf
bedrooms: 2 - 3
price: $103,000 - $200,000
finish level: complete, inside and out, including mechanical systems
features/finishes: wood floors, hardwood windows, steel tile roof, Bosch appliances
more info: brochure (pdf)