[T.G]

Yes, tin and copper both were commonly used to seal the humidors. Some humidors will also have a ceramic, like a thick tile, humidification element that one would take out periodically and soak in a bucket of water.

Addendum: tin/copper sheeting were also commonly used for quick conversion of things like end tables w/ a cabinet door into a humidor. So, depending on what you are looking at, it might never have been designed as a humidor initially.