[BrianG]

I have similar battery setup as yours and recommend putting some kind of angle pieces on the ends to keep the batteries from shift front-to-back. Even with straps, the batteries will shift enough to possibly interfere with the suspension arms.

Also, it looks like you are using round-head screws for the battery tray. If the metal isn't thick enough to use countersunk screws, I'd use fairly thick padding to keep those screw heads from wearing through the battery insulation and shorting them out.