replacing 2 12v with 2 6v question/again?

The more research I do the more confused I get. Recently bought a 2004 Minnie 32g. While going through it at the walk through I asked the tech to turn on all the lights when we started. About 20 minuets in the lights started to dim. The tech said no problem we will put in 2 new batteries(sure no problem the rig was on consignment and they probably charged the seller double). So they put in 2 batteries northwest 550 ca 24m batteries, so small they didn't even fit into the hold downs properly. I happen to have a year old set of GC2 Interstate batteries 6v in one of my small 60amp solar sets. It gets very little use and the specific gravity test I did today came back with one battery all three cells at 1.275 and the other battery all cells at 1.295. I'm pretty sure that means they are in great shape and charge.
I plan to swap them out with the ones from the dealer and am curious how much more use I will get out of these 6vs compared to the 12v ones. I cant figure the amp hours difference due to each batteries method of stating amp hours. The 12v s are rated 17.1 @ 5 amps and 4.9 ah @ 15 amps whereas the 6 volt gives the amp hours as 232 @ 20amps. I have read a quite a bit here on chargers, batteries inverters and convertors an it's all becoming a blur to me.
I will be dry camping mostly using gas for the w/heater fridge and some heat (catalytic heater with 1 pound propane bottles for the main heat) all lights are now led, 48 watt tv/dvd using a 100w inverter plugged into a 12v lighter in the tv cabinet and a slide and that's pretty much it except for the ghost load. I will use the generator for the microwave. I plan to charge with one of the Black and Decker 1093 portables off of my 4k gen. I also plan to change out the 7345 conv/charger with the 4600 series 45amp. this winter.
I guess this whole post boils down to how many times better are the 6v over the 12v system as far as battery storage.
Thanks