This Sky High 2/0 gauge wire is ridiculously over-sized. Normal 2/0 welding cable fits into the JBL no problem, this needed significant trimming. The wire split in half filled both the 1/0 holes in my toolmaker inputs. Would definitely recommend Sky High cable.
Still need to finish some things off but there's some thunderstorms coming and I have to get some work done tonight. Initial testing I'm very happy. It feels louder than I expected it would and the frequency response is about what I was after. Still need to really see how loud it can go and take a look at what flexing issues I have that can be fixed (with the vehicle, not the box). I do plan to carpet all or most of this and I'd love to add another battery or two if I can find room since I know voltage is an issue with that crown amp on only 4 batteries.
Will update from here as I clean things up more and do some real testing.
Thanks to Shocker Mike and Will at Makeitlouder.com for their great advice, and big thanks to Russ (Gumby688) for coming over today to help me with the things that I couldn't handle alone.