I realize this is a fairly old thread. But it is very close to my question, and the best I can find on the forum. Rather than starting a new, nearly identical thread, I'll post here.
I'm preparing to do a 3P4S build of 304Ah Eve with the new 2xM6 studs. Bus bars in general, and especially flexible, for these terminals are hard to find, expensive, and not available in configurations for larger paralleling configurations.
Like OP, this is going on a sailboat. I'll be building the pack in a tight box with modest compression, so hopefully no motion anywhere. Most of my connections will involve 6 cells, either with a long bar (6 terminals in a line) or with a short/wide bar (3 terminals down each side). Of course, each terminal is 2 screws, so double the number of holes.
I'll use copper, plated with lead-free solder. Copper will be sized appropriately for the loads (400A fuse on the bank, actual loads rarely over 300A), using the 30C column here
https://www.copper.org/applications/electrical/busbar/bus_table1.html (so 1/8x1.5 or 3/16X1 for the long ones, and the wide ones are a complete non issue).
Has anyone had any negative outcome from using solid bus bars? I understand the "theory" about solid bars putting undue stress on the terminals, but what about "in practice?"