I put the battery behind the right wheel of this truck at least 10 years ago. I had to replace the battery, so I thought I would post up some pictures of how I did it.
This is the battery box, made out of two of those heavy-duty shelf brackets (usually white), than you can find at the Home Depot for about $5 each. I also used some sheet steel that used to be the front cover of an old gas grill.
And side view
I welded a couple of pieces of angle steel (from an old bedframe) into the frame behind the right rear wheel. You can see the rear of the leaf spring at the bottom of the picture.
Battery box in place. I drilled a couple of holes, and bolted the box to the angle steel with 3/8 X 1 inch bolts and nuts.
Closer look, with battery in place.