There's always ways of covering the nail heads. Buttons or metal casting can be added on to the nail heads.. This was often done for hanging pictures in the Victorian era where they would cover the nail or screw or something with a decorative metal or another material.
Other option is construction adhesive onto a piece of Masonite.
Using sandbags to weigh down the tin to the Masonite to provide distribution of weight. Without having to use clamps.
Then you can use the Masonite to provide anchors that can line up with the studs.
You can also patch the holes in the tin with bomdo from the backside if you want smaller holes or hide existing holes.
Another option is to put strips of wood lath across the wall and anchor them to the studs.
Then anchor the tin to the lath straps..