Chris,
Definitely do NOT connect your batteries anything like the pictures depicted in the Forest River Forum posts. The owner has that all wrong. Lengths of cable between series batteries should be short. Length of cables between the paralleled pairs should be adequate. I didn't see any circuit protection, either.
I'd suggest to use the largest cable possible for hookups. This is not the place to save a nickel as you will have the most efficiency for the life of the installation. I'd suggest 2/0 cables and that includes the distribution to the inverter and converter. Replace them if necessary.
Heavy lugs are worth the price. The others are not very stout.
BTW, 80 percent inverter efficiency is out of the Stone Age. 90-95 percent is typical.
