rustup is pretty cool, but have you ever wished it worked a little differently? Maybe you'd prefer something that worked a little bit more like Java's Gradle, or Python's Virtualenv?, or you just want to make a custom environment you can scoop up and deploy to non-Internet-connected computers?
The Simplest Rust Toolchain Installer walks you through using existing crates to make a simple toolchain installer, and explains how you might customise it to meet your particular need or use-case.
Let me know if there's anything that's unclear, or could be explained better, or doesn't seem to work for you. I've tested the code on Debian Linux and on Windows 10, but there's always wrinkles somewhere. 