In the last image it looks like the left side panel is bulging a bit, any reason why?
There may be a slight "bulge" because there is a built-in tolerance for the vented panel to fit snugly over all the base units. When the screws are tightened on the top and bottom, you may find it raises the center. To avoid this, you could choose to not tighten the screws so much or place some tape between the panels to "eat up" the tolerance gap.
Another option may be to bend the mounting tabs for the vented panel outward which should also help snug up the surfaces.