Your going to have to find that inverter/converter as well. The batteries are only half the story.
Of all the systems in these RV's I'd say the house batteries are the most abused. Hate to see people purchase new deep cycle 6v house batteries only to find them flat dead a few days later.
Soooooo bad to run deep cycle lead acid batteries flat dead!
I had a 93 Pace Arrow Diesel for 12 years before our current rig. One of the first projects was replacing the house batteries, 4 six volts from Sam's Club. Back then about 85/pop.
Replaced some of the battery cables and also replaced the "charger", the Pace had separate inverter and inverter. Purchased a Progressive Dynamics 60amp charger with charge wizard pendant. Got 10+ years out of those batteries. Over half those years I did'nt have the rig plugged in during out NH winters! When I winterized I'd fully charge the batteries and disconnect the neg. lead.
That converter or charger should hum. Perhaps if you make sure its absolutely quiet and listen for a hum where you think one inverter is.
It should be very close to the batteries. Dont want long cable run from house batteries to inverter/converter or charger.