The hammond enclosure you have is correct and the waviness on the outside of the enclosure are pretty common. It's not really a "defect" but it's related to the molding process of the box itself. The inside of the box has actual ribs where you can subdivide the box up or glue in partitions, and the slightly ribbed outside it just waviness from the injection molding process. You can use a sanding block to flatten out the plastic, or when you paint the box use a filler primer and block the primer and the waviness will be less noticeable.

