UPD: Just use ZeroTier — open source, cross-platform, secure and easy to use virtual LAN. Add your remote computers to a virtual network and connect to them as if they are in the same LAN. Connections are end-to-end encrypted and P2P, so you always get the best speed and latency possible …

This one is similar to persistent local SSH server forwarding setup (although much more simple). Preparation part is exactly the same, so if you've already done that, you may skip it and go straight to persistent SSH proxy configuration.

After each file and command there will be a location label …

SSH keys come in pairs: a public and a private key. It might be easier to think of them as a lock (public part) and key (private part). You add public key (lock) to the computer you want to connect to, and then you can connect from elswhere and unlock …