Thanks so much! There are some excellent ideas here. My thinking now - based on everyone's thoughts - is to do the following:
1. Before I leave, charge the batteries to 80% and plug into shore power. I will leave the batteries on so the bilge pump can run.
2. Set the MV charger on shore power to a low bulk and absorption voltage - like 27V. I can do this easily using the Masteradjust software which controls all settings for the Masterbus. I will experiment first what state of charge this will result in. Should be close to 80%?
3. Get a mobile hotspot that runs of 230V in the boat.
3. Have my laptop running both Masteradjust and Teamviewer connected to the hotspot. The laptop is running off a 230V outlet.
Viola, with this setup I should be able to monitor the batteries and control the charger from my home in SFO while the boat is in La Rochelle! So I will be able to charge to 100% every three months by changing the setting for the 60A charger. I will also run a dehumidifier over the 230V outlets in the boat - Scott, presumably you didn't have shore power which is why you ran the dehumidifier over the inverter? I had a dehumidifier running during the entire 18 months of Covid layup and it made a huge difference. If there's something wrong with the 230V, I will know because I can't connect to the laptop. Lastly, I will have a Netatmo security camera and a WIFI enabled water alarm in the engine room connected to the hotspot. That way I will get emails if something moves inside the boat (and will be able to see video of the event) or the water goes above the alarm level in the engine room. My boat watcher will not have to deal with the batteries at all if all goes accordance with the plan!
Currently in Ile d'Yeu, France