Cozzie homes build MEGA nice shelters. He does have a bit of a waiting list (you wont get one within a week) BUT they really are built to last, and he will design whatever you want, however you want, and delivers pretty much every where.
I looked around for a mobile shelter several years ago but couldn't belleve the extortionate prices. I showed a local joiner what I wanted and he made on for me for £500. Making a saving of £700! 8 years later and it's still going strong, has been moved goodness knows how many times, and I would be at a loss without it!