Vanaroo said it best, "So many variables... hard to give a definitive answer".
It does;'t need to be that complicated for what you want to do. I strongly suggest that if you use your primary battery hooked up to others, you use an isolator so you don't run down your primary battery. Also, it was correctly stated that the fridge is the biggest draw. I don't know how they came up with the amperage, but at 12 volts, it can be a lot. I strongly, strongly suggest you consider Odyssey AGM batteries. They are better than regular auto lead acid batteries for your intended purpose, and Optimas are just overpriced junk. Depending on the amount of space you have for batteries, you can use two smaller PC1100 batteries (two of them weigh about what 1 regular car battery weighs, or you can go up to a standard group 31 battery at 100Ah each.) I wasn't really sure how the 50% use was calculated because you can choose batteries that run from 45 Ah all the way up to over 100Ah each. Also, if you draw a charge from your main battery, you want to use a low voltage cutoff. You can buy one for $15 or many inverters have them built in. Personally, I think you can run a 12V to multiple-bank-12V charger from your main battery and simplify the whole thing. NOCO makes a charger that has multiple banks, a low voltage cutoff, and runs from 12V power. (so it's 12 volt input, with anywhere from 1 to 4 banks of 12V output, and all the electronics are included so you simplify the whole thing) You might want to look at how fishing boats use multiple batteries. The use is very similar.