Hate to dampen any bonfires, but it's too old and obsolete to sell as a gun cabinet. As a bare minimum they have to be 14 gauge steel, with internal hinge pins and anti-jemmy flanges, capable of being masonry anchored to external walls, and have a minimum of two seven-lever locks.
I'd keep it and put my porn scrolls in it personally....... I have non-slip soles on my slippers