Check out this amazing tech-heavy breakdown with Aleksandrs, mask and weighted normal workflow!
https://gamesartist.co.uk/old-freight-car-prop-breakdown-aleksandr-silantev/
Aleksandr Silantev, 3D Environment Artist, has made this huge breakdown on his Old Freight Car, he explains in full detail how he created this prop using weighted normals and a mid-poly workflow, he runs us through an advanced working with masks, Vertex coloring, complete UV Unwrap, Baking, texturing with Substance, creating a master material and decals.
https://www.artstation.com/artwork/L3dNal
https://www.artstation.com/sanekum