The lab I worked in had a vertical steel wall which was 18' high by 22' long.
The biggest single print was approximately 18 to 19' long by 6' wide. This was the largest colour negative roll paper made by Kodak. All paper on this wall was held in place by magnets, lots of them and all placed in position in total darkness.
In the centre of this wall was a special clip-on section where we could attach a square 6' steel vacuum easel. This was used, mainly in B&W printing, for adding specialised borders to prints. The vacuum held the paper in place and the borders were held in place by magnets. The borders were just strips of thin metal.
I can tell you that the vacuum system was good news and bad news. The good news, the suck was so strong that paper didn't move a millimetre. The bad news, ever tried to carefully (without making kinks) remove paper the instant you kill the vacuum?
Mick.