Ideas for Data Transfer/FTP Server?

HI EVERYBODY.

So I have this bunch of scientists and, like always, they need to send a bunch of god damned data. The data is raw image files, typically about 100-300GB.

They need a method to send this data across the internet(they visit remote sites to collect the data)from the Linux CLI without requiring their host sites to install any special software.

I have a static IP available. I'm thinking it might be wise to set up a linux STFP server outside of my firewall, give it a static IP, have it store the data on a portable drive, and then move the data to a drive inside the firewall. Because I don't know what the incoming IPs will be, iptables are unsustainable.

But having never created an FTP server in Linux, I'm a little spooked about security. Web-facing things make me nervous. Because of that, I want to retain the air-gap between it and my network.

So where do I start, and can anybody recommend an EASY way to accomplish this? I prefer Debian or CentOS, for what it's worth.