lead acid batteries are 12v
lead acid batteries and will work the same with chargers and maintainers and provide about the same energy per weight no matter whether you are using sets of 6 cells in parallel or just a single string of 6 cells in series.
An intellipower with charge wizard is an excellent way to charge and maintain an RV 12v
wet cell lead acid battery system. For best life, don't make a habit of going below 12.2v as measured after the bank has been sitting with no significant charge or discharge for at least a half hour and do recharge promptly.
2 batteries, such as T105's or group 27's will handle about 40 amps max charging rate so let that guide your sizing decisions.