Thanks to Don, who pointed out that my plan for securing my battery box didn't meet the rule book requirements-- so, plan B.
I cut a length of 16 gauge 1 1/2" x 3/4" mild steel tubing and welded a thick cap on one end. This will lay across the top of the battery box. That end cap has a 3/8" hole that matches a similar hole in the side hold-down. This piece is 0.050 6Al4V titanium with a doubler plate of 0.095" 7075-T6 riveted to the top edge. The rivets are CherryLock CR2653-4-4 which are A286 alloy. I fooled around with the rivet puller nose to see how much it changed the stem break depth so they look a little different but the stem is staked in place in all of them. The bottom edge is drilled for 3ea 1/4-28 bolts which will thread into Nutserts which I'll install into a chassis tube later.
The 3/8" holes are for stainless quick-release (pip) pins that will allow the battery box to be removed without much effort.
The zinc chromate primer is still drying on the angle that will secure the battery box laterally but I did get the holes match drilled in the bottom panel today. The Paint on the battery hold-down tube isn't dry yet either so no pictures of those pieces today.
BTW, the faint lines on the Ti sheet is a pen mark, NOT a scribed line. Never scribe layout lines on sheet metal that is going to be used in a race car or aircraft application. As Carroll Smith said, "It indicates where it will break."
Regards, Neil Tucson, AZ