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."