OK, so you are using 8D size 12 volt batteries -- the big 190 lb ones ! Each of these is about the capacity of three normal RV deep cycle 12 volt batteries, so you do in fact have the equivalent of the 9 batteries I first asked about.
That gives a total of 570 lbs of batteries so I guess you have a good place to mount them and they just subtract a bit from your cargo weight to keep your rig within its load limits.
They do OK when charged/discharged in parallel if they are the same manufacture date and same brand and in the same condition. Charging them optimally would need about a 90 amp converter, so maybe your rig has more than the 60 amp unit most compact RVs have. Notice I said "converter" which is the appliance that makes 12 volts out of shore power and runs the lighting, furnace fan, etc and also keeps the house batteries up when at a developed campsite. All modern RVs have a converter, but many as you note do not have an INVERTER, particularly the 20 year old ones like yours.
To find an INVERTER if it is in your RV now, look for heavy gauge wires at your battery location that go to an electronics package -- these will be AT LEAST the thickness of car jumper cables since they need to carry large currents. How large? If you have an inverter of 2000 watt continuous 110 volt AC output (and presuming it is at least 85% efficient...) it will draw 196 amps continually from the battery bank at that output load. Even with your large battery stack, that amounts to a "5 hour" discharge rate...meaning it could provide this 2000 watts for only 5 hours before completely draining all charge from your batteries. Clearly you want to load an inverter with lower wattage loads and for sorter intervals -- this is why the RV air conditioners are not run on inverters.
The large inverter in my 43 foot long diesel pusher coach was set up to run the residential refrigerator (an intermittent load of a few hundred watts), the microwave (again a short duration use) and the TV. It did NOT run the washer/dryer, the air conditioners, the diesel engine block heater, etc for obvious reasons. It also had its own dedicated battery bank so it could not deplete the house battery bank or the engine starting battery bank.
If you find you do not presently have an INVERTER in your RV, there are many brands out there targeted at small vans through larger rigs. The solar industry has given rise to reasonably priced units. Some are inverters only -- others have battery chargers and management systems built in. Watch out for peak versus continuous ratings, as some inexpensive imported units are not meant to run a long duration without getting quite hot. The heat sink ribs on the cases of any inverter without its own cooling fan built in should be an indication that they need to have space around them and adequate air flow...
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