Do you have a welder or someone who can weld for you? Cutting the right side of the rollbar about an inch down from the top and rotating it counterclockwise 90 degrees will give you some more room for a battery tray. Some guys cut the right side bar and have it run to the rear of the truck, I think that's how the electric roll bar from New Era comes.

Either way I don't think your tray is going to fit on the main chassis. It's going to have to be mounted further forward and up higher over the steering servos a bit. So you'll have to make some spacers to go under the tray. If you go with an XXL chassis you will gain a little bit of room (about 1/4 - 1/2 inch) in front of the rollbar as it sits.