This follows on from some research I did into starting a business selling advertising space on bikes with trailers or on specially constructed tricycles or quadricycles. The picture is from Gotcha who can be found at Ad-bikes.com.
Eventually I found one company "Work-cycle" of Holland who would be able to let me have a trailer mounted advertising system which uses A0 sized posters. My stumbling block at the moment is the cost: Euro 950 each plus delivery. Work-cycle are listed in my links on the lower right hand side of the page.