you are correct... they are 4 6v batteries. 2 wired serially (positive to negative) to make "one" 12v battery. this is done twice so you have "two" 12v batteries. then the "two" 12v batteries are wired in parallel (positve to positive and negative to negative) to increase Ah capacity. once this is done, you have a bank of batteries that you treat as "one" battery.
you take the negative and positive that are furthest from each other in the bank to provide a balance drain across the entire bank.
take a picture of your battery bay and we can tell you exactly which terminal posts to connect to.
on mine, they were not wired correctly, but instead they used the shortest battery cables they could. made for a neater looking wiring job, but will lead to premature battery failure because of it. it'll work, but it's not right... i'm in the middle of fixing this...
himcules (10x stronger than hercules)
2013 Forest River Berkshire 390BH-60
ex 2007 Jayco Greyhawk 31SS