I installed my new battery box parts this morning, I got the idea from someone else here on the forum.
Our 1972 Sovereign
is a center bath, and has the battery box under the range in the kitchen. Originally it was sized for 1 group 24. I had stuffed a group 27 battery in there for a while, and it sort of fit. But I had seen a reference to taking out the part of the inside of the door and running 2 batteries in the box. to do this the box has to be expanded to reach all the way into the frame rail. I took some measurements, drew up some parts. and Voila, new battery box.
I modified the door to remove the original space filler/ support piece of plastic, and adding strips of aluminum to fill the gaps, and reinforce the skin, then buck riveted it all together.
To fit the batteries, I need to add a spacer to lift the batteries up about 3/4" and get some trays to catch any errant acid. I'm still debating on cheap plastic trays and strap hold downs, or making a stainless steel tray to fit in there.
The nice part of it is, it doesn't really take much more room than the original, I may have to mount the water pump directly to it instead of the plywood shelf it had before, but that will be fine. the aluminum box lid is plenty strong enough. I think I'll add two bulkhead connectors in the back center for the wires to come through to seal the batteries from the inside space a bit better than the factory version.
I also grabbed a scrap of UHMW to line the inside of the lid to keep sparks from happening accidentally. I'm leaning towards clamping the battery cables on, and using an Anderson connector for each, kind of like the factory battery disconnect. That way I can unplug them, pull out the batteries, then deal with the cable clamps outside of the battery box.
Here's some pictures, if anyone else is interested, I can supply dxf files and dwgs for your local fab shop to make you your own, just let me know.
Picture 1 - parts made
Picture 2 - Parts riveted together with old door Modified
Picture 3 - Installed. inside lid still loose,