With metal cabinets there isn't any note of it needing to be listed/approved, or the cover either. Just that it essentially be painted or galvanized, and at least so thick...
312.10 Material.
Cabinets, cutout boxes, and meter socket enclosures shall comply with 312.10(A) through (C).
(A) Metal Cabinets and Cutout Boxes. Metal enclosures within the scope of this article shall be protected both inside and outside against corrosion.
FPN:For information on protection against corrosion, see 300.6.
(B) Strength. The design and construction of enclosures within the scope of this article shall be such as to secure ample strength and rigidity. If constructed of sheet steel, the metal thickness shall not be less than 1.35 mm (0.053 in.) uncoated.
I know a company here that will make, if you like any box, gutter or cabinet you like. Even rebuild tranformer cases, and sent the windings out to be rewound. Myers sheet metal - formerly part of Myers electrical products but spun off eons ago. Now just a small shop downtown.... I occassionaly get them to make me stuff.
Anyway, what I have seen before, and wish they weren't so hard to special order, is divided gutters that constitute two wireways....
