Finished retrofitting the 45-degree circuit board panel. Installed nutplates, double-checked everything & buttoned things up. Performed one more final check that the bus bar wrap laid where it should & then applied power. No smoke this time. Hopefully, it stays that way, but I'll be keeping an eye on this problematic installation.
Down the road I may design a simple 3D printable plastic back shell that the entire board can be housed in & then installed into the stock vertical or the optional 45-degree framework. As my dear father always told me: "If you want to be safe, wrap it..!"
For the next assembly I will seriously consider Vertical Power's VP-X Electronic Circuit Breaker System in-lieu of traditional breakers.
