The OP mentioned modern battery technologies - generally the shunt sits between an LFP battery negative and the main circuit negative/ground, and the solar panels connect to MPPTs. So the voltage at the shunt is a nice consistent nominal 12.8V (~13.3V in practice) or a multiple thereof (for series battery setups).

I just upgraded our hybrid caravan to 24V LFP (2x 300Ah 12V), roof solar + extra MPPT for external solar, shunt, inverter-charger, 24V->12V converter for existing circuity (lights, pump, etc), DCDC charger from car, battery balancer, a little touchscreen interface inside (all victron gear with renogy batteries). It was as a lot of fun and it's amazing how much power we have off grid now! The system would work excellent for a little cabin exactly how it is (minus DCDC).