Two 6V's will get you more amp hours and last longer, but the point about one failing and taking out the entire system is a good one.
Our 130W of solar with two 12V's has worked for us over the last 15 years, but I only need 3-4 days at a time without shore power, and at least one of the generators are always with us just in case. We don't do as much winter camping as we used to, so if we need heat for a couple days, it's either propane and a lot of battery draw, or we run the generator and electric space heaters.
BTW, as for sunk costs and the generators... Last night our house lost power in freezing temps, and those sunk cost generators gave us a lifeline for the six hours that it took the power company to fix things. One powered up the coach with space heaters, and the other was hooked up to our sump pumps and selfishly, the DVR to record my football games. I was in the process of splicing into the furnace wiring (house breaker off) just in case the power wasn't coming back until morning.