Just starting new rear boxes:

Bending metal with break thingy...

Rubber mounting, I got some flat rubber , kinda looks like tire rubber but has thread instead of steel inside it.

Unexpected Feline Supervisor:

comparision of welded boxes to bend metal with no sides yet:



I cut a massive hole in the rear trunk area sheet metal of my Cortina, where the old gas tank hole was. The new much larger hole runs in-between the leaf springs and just behind the rear differential.
Cut, bent and welded a bunch of 16 gauge steel sheet (wore a respirator for the galvanized pieces). Thus creating 5 horizontal boxes which hang down 5 inches from the original trunk floor. The boxes hold horizontal parallel rows of batteries, which finally appear like one square pack, except for a small gap for the final row making room for the leaf spring shackles.
The leaf does not pass under the boxes, the edges of both are 1 inch apart.
I also removed the leaf springs and delivered them to Denver Spring company to have one leaf added. I had previously lengthened my spring shackles which made my car driveable but the leafs were flat, not good.
I have not painted the boxes, some are galvinized which helps but some are raw steel and need primer. Plus all the cracks etc need foam padding and/or some method of sealant.
Then finally a magic wand is needed to create "the perfect lid", for starters that will end up being some plywood lined with foam from the battery shipping boxes.