50 kb/s x 1000 bits/kb x 3600 s/hr x 24 hr/day x 1 byte/8 bits x 1 MB / 1000000 bytes = 540 MB/day. That's enough to download VPN software and a Linux distribution to run it on in a day.

If you've already got a Linux system, the Debian openvpn package is under 1 MB and at 50 kb/s would take under 3 minutes to download. I don't know if openvpn in particular is suitable for people who are trying to evade their government, but would whatever features it is missing add substantially more size?

Yeah, you could use forward error correction too, so any n bits would be enough to reconstruct the input.

Of course then you get into needing software to decode the more advanced encodings; maybe start with a voice transmission explaining in plain language how to decode the first layer, which gives you a program that can decode the second layer, or something.

Starting to sound like an interesting project.

You never used dialup did you?

Wireguard ships with the Linux kernel so you only need to receive ~60 bytes of configuration information.

HF are really noisy. You need a lot of error correction to ensure that the package is consistent and without any error. This will drastically decrease the real bit rate.