Opie, I wonder why you have this many batteries. I don't know what kind of camping you do, and / or how you plan to recharge them. If you go camping for a couple of days and then use shore power to recharge via the factory converter / charger? I can tell you the low charging voltage as well as the inability to program to match the needs of the batteries is problematic for these cheap units. Both, in performance and providing long life to your batteries.
The first thing I would add is a good monitor and Trimetric (such as the TM-2030); without one, you will be guessing how many AH you are using or when you need to conserve or charge. This typically requires either a 100A or 500A shunt in series with the negative side to frame ground.
I would also add a 300A catastrophic fuse on the positive side.
I would also suggest getting a marine type switch that allows battery string 1, 2, both or none to be switched and connected to the negative side. I reasoned the switch or a cable if contacting the box will be less harmful that if a + was to contact. It is handy to cut all power or to only one string for maintenance.
The shunt size depends on the total amp load, whether charging or using. At around 800 A and below get a 100A shunt; over that use a 500A shunt.
You question about the wire gauge size to the WFCO, I would go with a #4. Again, in my case I have 75 Amp charger in an Inverter and don't charge across this small cable. But, I have the factory Converter / charger in place but switched off "just in case" I ever need it.
BTW, charging can be accomplished with a good charger in several hours via shore power or generator, but the time frame drove me towards solar to do this. The factory converter charger could take, actually, days to get to maybe 90% full, while PV is doing this silently and for very little dollars, over the long run.
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