Personally, I don't mind the thin shelves inside that safe. Granted, safes generally contains cold bars and stuff. But a lot of times, it just stores cash. Thinner shelves allows for more of them and thus more cash.
However, you got two of them. You could basically just attach some vertexes to each of those and just give the illusion of them being thicker. You don't need to add more than 4 vertices, tops.
Nice use of ingame textures though. ;P