This week I found a few spare moments to finish the upper rear rack by adding a cage around the top which will hold polypropylene sheets to enclose the batteries. Here is the design done in Google Sketchup (PDF version here):
I cut the pieces mostly out of 1" by 1/8" bar / angle stock - the cage is not really structural (other than under tension to hold the top on):
Here it is, all welded together:
And placed in its location:
Still a couple of things to do to this rack: it needs the nuts welded on for the top hold-downs; it needs a hole cut to allow the 4/0 welding cable to exit the box; and, of course, it needs to be painted.