[GUI]

Could you use one chain for both wheels? Or have one of the wheels offset a little so you could put another sprocket on the gearbox and have it go to the same side on the second wheel?

The toughbox will be fine without a supporting bearing as long as there is not a lot of load at the end of the shaft (i.e. cantilever wheel maunted directly on the output shaft, or sprocket on the end of the shaft and the chain wayy too tight). The Banebots needed a support bearing because the shaft was so long, and the nature of planetary gearboxes meant that it wasn't supported as well inside the gearbox.