Ah the battery box. Alot of time searching and thinking about suitable battery holding went into this, until I found this in my backyard. Metal is heavy, stock battery boxes are fragile, don't have the tools to make my own out of a block of plastic. This is the top grate from an irrigation valve box. I used a reciprocating saw to cut it out of the top, and then a dremel to remove any hard edges and one of the cell walls. With padding, it is just about perfect for stick packs, as well as alot of lipos (adjust padding size). I think the inside dimensions are 139mm long, 54mm wide, 45mm tall. Only problem, green color, which doesn't bother me.
It is held to the chassis with machine screws and t-nuts, which are flush with the interior of the box. There are nylon washers keeping it a few mm off of the chassis to account for the raised sides of the chassis. Screws are countersunk into the bottom of the chassis. Foam is glued to the inside of the box to snugly hold the trakpowers (no heat issues, they barely get warm to the touch). They are held down by a rubberband held in place by two thumbscrews held to the sides of the box the same way that the box is held to the chassis. It is basic and nothing fancy, but it is extremely strong and durable, and can be modified very easily. This is a first try, as I will be making another box that will be more cleanly modified.

The chassis is narrow, but everything fit together easily.

Power is awesome. It is pretty close to a scaled up version of my RC18T with a mamba 6800 and 3S lipo (= almost uncontrollable). The trakpowers make it all possible. Tops out over 40mph even with 16/46 gearing, due to ballooning of stock tires. Have some proline CF MTR's on the way, along with diff oil setup this way F/C/R: 7000/50000/5000, to reduce balooning of front tires. Ballooning of front tires under acceleration is absurd, hence the syrup in the middle diff. No steering problems due to JR 9000T.

Only problems so far: I run primarily in grass, so overheating of the MM is an issue, but I do not have a fan yet. The batts stay cold, motor stays warm, MM gets HOT, but it was never designed to handle this setup. I don't know how hot since I do not have a thermo.

I have some video before putting oil in the diffs, but will post some when I run it with the current setup.

This was an easy conversion due to the machining of Mike and the experience on this forum. Thanks to everyone.