There are a couple of things I can thing of. Either getting straps to tie around it, or VHB tapes.
I think the best solution if long term and depending on what you are using the container for is to drill holes in the the container and use nuts and bolts with big washers to go through the eyelet of the banner and then the metal container.
Will or does the banner have eyelets?
The administrator has disabled public write access.