Hi, There are not so many trucks in the UK now with Flatbeds but the cover was known as a sheet, On a 40ft Trailer depending on the load you were carrying we had three, two main sheets and the last one was called a fly sheet, this was at that time made of plastic and was 40ft in length, you started by putting the rear sheet on first, tie it down, then the front sheet, depending on the load you could get the load to look like a parcel on the trailor, At the rear of the tralior, you, depending on your experience, could wrap the sheet like an envolope.