@Dads203 : interesting knowledge, thanks
Given the dry climate where the original tank seems to be stored, rust will have sober and dark tones, with minimal leaking. We'll use mixes of SDW Shading Color TESC60 Drab Grey, with Rust SDW 01 and 04.
Both ranges are blendable, but SDW Shading Colors are more opaque, while Rust SDW are more blendable. I've used different proportions upon the need.
Here, more paint into the mix for the initial touches :