I am worried about your new battery tray...
I managed to snap a piece of welded aluminum on my battery tray. I am concerned that all 4 sides are just folded up, perhaps you could epoxy/jb weld them together? (I am just thinking a closed box would be stronger). Perhaps I am overly cautious, but that looks like a heavy battery... if the outside wall of the box bends down that is would be a large dangerous flying object.