I just replaced the house batteries in our Sea Breeze after getting 8 years out of them. It had to 6v in it. Just curious, why do some people run two 6 volts instead of parallel 12v?
It might also depend on your use case. I initially started with a bank of 6v Trojan T-125's, but wasn't satisfied with the voltage drop on heavy inverter draw. I switched to Rolls-Surrette high capacity 12v (210AH) to help mitigate that issue for me.