I just installed a Victron BMV-712 Smart battery monitor on my off-grid system and I plan to install one in my Airstream some time in the future. I have documented the installation steps and some detail on adjusting setting and using the smartphone and computer (Mac OS & PC) free apps.
The video describes a 24 volt system and your Airstream is 12v but everything else applies directly to any solar system and battery monitoring. https://youtu.be/vHIZ-EA9y6E
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