So I feel like there's some files missing from https://umod.org/games/rust
When I unzip the file there's only a 'Managed' folder in the RustDedicated_Data, no .bat file that tells the server to run Oxide, no oxide folder to load plugins into. I've watched a few Youtube guides and I've scanned this website for the base Oxide mod, but I can't find anything. I've also looked for the Oxide mod discord, no luck there either. 

Any advice would be appreciated.

The "oxide" folder is created when the server is first started successfully with Oxide installed. The .bat file is not part of Oxide, that is something you'd setup yourself as part of your normal server setup before modding it.

For the Discord, we do not provide a public Discord for support. Our forums are here for general support.

Okay I've ran the server several times after installing Oxide (i.e. just extracting the file and overwriting the files in the Managed folder), but I'll try again.

How are you running the server? If you have a startup script that runs SteamCMD each time, that's likely uninstalling Oxide.

That's a very good point, thanks. I'll give that a try now.
Edit: Yeah that was it, thanks a lot!