RS4, you know, I was thinking, and even though you may not be able to use the "velcro on the chassis" idea, you could still easily use the same concept by running a strip of velcro the length of the battery and using the velcro straps with the mating side facing the battery. I used this as a temporary fix on my frog when I somehow lost the battery door and it worked perfectly--and that's with the battery hanging off the bottom. I did a little sketch to show what I mean...