Your rig impresses me every time you post about it
I can't imagine using that much power - but we honestly don't spend much time in the camper typically - either out and about or at the campfire. Weather forces us in (like it did last weekend) and we use a bit more, but even then just lights/water and the phantom loads. If it's the wife and I we read and talk and if friends are taking shelter with us we play games typically. Also charging and playing with gadgets - but nothing like your entertainment system. When we get to the point where we spend more time on the road, this will change....
But, yes, your numbers add up.
Total AH 255A
Daily -48A 2 amps @ 24 hrs
Night -60A 20 amps @ 3 hrs
If anything, you are a bit above 50% used (255A/2 means 127.5 is the half way point).
The voltmeter test for capacity is marginal at best (but is what I use). The amount of load on the system at the time of measurement and "rest" time seem to have a pretty big impact on the battery DC voltage reading as well. They say, for the voltage test to be accurate you have to disconnect all loads for a few hours, and then take the reading. Clearly not practical while camping!
I've been considering a Trimetric RV meter. This system uses a "tap" to accurately measure current in and out of the battery bank and thus let you know where you stand. The solar guys love them, but from reading they perform well for us generator guys too. Although your "dual bank" system would complicate that as it wouldn't' know which bank you are on. I'd think you'd have to have 2 of the damn things which probably isn't realistic.
At the same time, I mostly weekend so with the current system I can get through a long weekend without the need to haul the generator or have concerns about staying warm at night. (Memorial Day week, 4 of our nights will be sequential without power and while I'm not convinced I'll need it, we will be taking the Honda 2k)
Obviously you've built a great system for high power demand off-grid camping. I am curious why you use GP24's as opposed to golf cart batteries? I'm a believer in getting the most amp hour in the least space/weight for the least cost. Costco GC batteries fit that bill for me, I think I have around 225AH with the two of them. They are a bit bigger/heavier so that is a consideration, but hey, 4 of them would nearly double your capacity!
Anyway, thanks for reaching out.....