On Saturday, 4 July 2015 16:54:36 UTC+1, David wrote:
Something like http://www.big-wheelbarrows.co.uk/5-
flatbed_turntable_truck_ht1101.htm would do the job, but at around £450
this is way over budget and also it is a big item to transport and store
to/from the parking near the site.

They're available for hire

http://www.hss.com/hire/p/large-4-wheel-turntable-truck

Would it go on a roofrack above a car for storage and transport?

A possible alternative is to borrow a horsebox or similar and leave it parked at your exhibit location. Drop the tailget when 'open' and lift and lock it when 'closed'.

Owain