I spent some time with a co-worker of mine named Tim (no relation), welding up the steel that I've spent the last 3 weeks cutting up. When I say I was welding, I mean that Tim was welding and I was standing around staring at the ground so that my retinas wouldn't turn to cinders inside my eyeballs. Tim very graciously agreed to weld up the battery box supports as well as some of the other structural stuff yet to come. Here's a look at three of the frames he welded up. All around nice work.
Here is how the battery box will fit in the frame. Snug, but a bit of room to move around if necessary.