It seems everybody using FB has it's own recipe to make it flat. I am fixing the paper with clamps between wooden frames and glass.
With this method the paper becomes very flat after drying - I'm quite pleased with the result. The only drawback is that I need to cut the borders because the pattern of the frame remains printed on the paper surface.

I'm thinking whether it would make sense to mount the paper BEFORE exposure/processing?
I could use 3M photo to mount the FB on 2-3mm thick sheets of aluminium.
What do you think of this idea? Could there be problems during developement due to reactions with the metal / during washing due to the impermeable back? Could the durability/stability of the image suffer?