We now have a (rather good) LAN on our boat – but the last challenge is to access the computers on the boat.
4G networks do not generally hand out a IP address per endpoint, not even a dynamic IP address. So other means need to be used, and I stumbled across https://remote.it/, which has a free service for single endpoint use.
And they supply their own management apps for MacOS and IOS etc., or you can use other protocols (including VNC) to access the Raspberry pi.
I have just installed it, and will move the Raspberry Pi to the boat this weekend. As a matter of fact I will move 2 Raspberry Pis there, one to be a Plex/Kodi server, and one to manage our power devices – as we supply power from batteries/solar panels/generators/engine/shore, and it all needs monitoring to ensure it works correctly.