Rust for rust

[jwb]

If it were me, I'd try going over the sides again with a wash of black, but for CTRN cars, those are pretty contemporary, and you'd want to add conspicuity stripes and graffiti. Here are a couple of C&NW cars as examples -- they're black, anyhow.    
   
That would both tone down the too-defnite rust and distract attention from it, too. The insides are fine.