Many thanks to all posters of content. Hoping to return some karma....
Getting ready to do some extended boondocking and decided to upgrade my Group 24 batteries to Group 31 AGM's. (going from 144 to 210 Amp/Hrs )In preparation for this I also upgraded my converter to a multi-stage Progressive Dynamics (so as not to cook the new batteries ;-)
This project was inspired by a youtube video by "Embracing Detours".... See link.
Having the advantage of doing this at home with all my tools and "Amazon Parts" the major change to what he did was the elimination of a bolted on angle at the hinge side of the box. I chose instead to create a double-articulated hinge, ordering an aluminum hinge off of ebay, modifying it per the picture, and then riveting it to the location of the cut-off "lip" on the box. I then riveted the old hinge/lid to that. Folds completely out of the way to take out and/or replace batteries. BTW, Group 31's added to standard box fit with 3/16" to spare, front to back dimension.
Photos from upper left going clockwise are... 1) before Group 24's 2) Battery box with lip cut off 3) modified Aluminum piano hinge 4) view of "double articulating" hinge 5) upgraded converter 6) new 31's in box. Tiny box in upper left of photo is a remote bluetooth battery monitor which seems to work just fine. Also moved and changed electric jack fuse to a car style fuse.
All rust seen in in photos was removed and repainting done.
Hope this helps someone.