Mobile shedworking atmospheres are always intriguing and I particularly like the mobile post offices detailed at the The British Postal Museum and Archive site (above is the cover of an advertising booklet for new Mobile Post Office service, published in 1937). Here's what it says:
"During the 1930s the Post Office decided that there was a need for the provision of telegraph, telephone and postal facilities at special events. It was felt that an 'office on wheels' would best meet this need, at race meetings and shows held at various locations around the country. The need for manoeuvrability, safety, space and economy dictated an articulated vehicle. The towing unit was a Morris Commercial Leader 3 ton tractor unit. This was given the registration index 'GPO 1' (these particular letters were allocated to the Post Office for use on 'special' vehicles)."Inside, the trailer had three windows for dealing with the public, two telephone 'cabinets', a generator, teleprinter, counter, stamp machines, letter chute and mail bags.The design has changed a couple of times over the last 70 years. In 1984, they introduced the 'mega-unit' (pictured above), more like a traditional shedworking atmosphere that had an exhibition area and separate hospitality suite: it could be moved but it was more shed than trailer.And since 1996, a smaller green-liveried van has been in use.