Easiest way is some super strong velcro on the battery and tray... Then some foam - i use a cut up shoe insole to pad the gaps. ATB... Sorry no pics to hand...
You can use the optional traxxas hold downs made for lipos I use 2 8000mah lipos or you can use velro straps and cut slots in chassis too...
how do you like those motors. I am looking for some brushed motors for my brothers new emaxx and he wants something fast and cool running. about how fast do they go on your setup.