I'd also look at outback carbon foam batteries.
I believe firefly now makes G31 and an L15 jar. The L15 is available as a 2 volt @ 900 amp-hours and a 4 volt @ 450 amp-hours.
G 31 is $486 and 100 amp-hours or $2916 for 600 amp-hours.
L16 is $659. Or $3954 for 900 amp-hours
https://www.bruceschwab.com/wp-content/uploads/sites/86/2018/04/Firefly-handout.pdfHigher voltage is a goal as well.
The link the OP gave does target a "package" that Battle Born sells so the PD converter is recommended by them.
I don't see 800 watts of solar as massive.