Not sure about Bitvise SSH server, thanks for the recommendation though, is that Zerotier works behind firewalls. Don't need to do any port forwarding etc. Very similar to Logmein's Hamachi.

Since their laptop is usually on WiFi behind an ISP-provided router/modem combo this is ideal. Also don't need to force a static IP on the network so the port forwarding rules align properly.

As I say, we're in different countries so this is very handy, it "just works".

Also is secure as nobody can jump onto the virtual network without explicit whitelisting on ZeroTier's Web UI. You have to login (with 2FA) and click a checkbox to allow access if anyone wants to join.