I had a new 7X5 shed delivered to site a month ago with no problem at all - there's no mobile reception but they arrived on time and met me there. This was a local company in the South West called Shed Scene - I arranged in advance that there would be some carrying involved and paid £20 extra, this was fair enough as it's uphill, a fair distance, and quite difficult terrain. We'd put the base in already and then assembled ourselves in less than 3 hours. The company said they frequently delivered to allotments and were very happy to do this.
One slight niggle was that only one key was provided and they can't be cut at locksmiths as a funny type.
I'd agree that a local company probably know the area and the site. Our allotment site is down a track that not easy to find but they knew where they were going.
My friends want to talk about their clothes shopping and don't understand the pleasures of a new shed! I'm sure there are some folk here that understand....