I agree with Freaky; a thin, light coating of dust, with a tad of grime in recessed areas and along the edges will break up the flat-colored-ness of the cargo containers.

Also, after looking at pictures of freight containers, yours look a little to long, in proportion to their height and width; here's some images of what I mean.

https://narrowmind.railfan.net/WPYR/f..._Container.JPG

https://www.chinamaristar.com/product...de_freight.jpg

https://www.intermodalsolutions.com/I...orage%20L2.jpg

Other than that, I think your textures look great; keep at it!