[Arnie.d, because your cover's spine is just plain black no one really needs the original Photoshop file to produce proper slimline cases.
I know but it is much easier.
I often have multiple versions of a cover in one psd. I really like the layers in photoshop. I have for instance multiple poster art, different backs, different spines, different logos in one psd. That way I can make a combination by selecting layers and print whatever I want.