Personaly I would have 3 banks fused at positive and negative ends if terminals are exposed, if not exposed then just the positive end, reason, if something shorts across two banks but not at an equal voltage point then the negative fuse will limit fault currents.
I know we all believe we it will never happen.
I had 8 banks of 2V batters for 10 years and ballance was never an issue, I know it is in text books but in the real world one checks individual battery voltages and specific gravity and equalises if required. Sure some of my banks received/gave more current than other, principally because of their age but the system voltage is what works for me.
If one had two water tanks, say one was 1000 gallons and one 2000 gallons but the same height at the base and top, connect these together and draw water off, they will give their share at aproximatly 2:1 within the connecting pipe limitation, equally batteries within cable limitations (resistance).
With more than one string you need to be prepared to monitor your batteries which will show up any discrepencys before they become a problem, even in a single string monitoring mid point voltage is a valuable tool for indicating any discrepancy.
Just my perspective from an old fool who has done it.
regards Allan