pic: Gear Drive Concept

[Joe G.]

If the bottom is even further pocketed, you're going to have structure problems with or without a bellypan -- with dramatic pocketing, there's no easy way to mount the bellypan to the box except at the ends short of welding it, and the bellypan itself would need to be heavily pocketed under the gears, and would provide only marginal reinforcement.

I would suggest using a larger tube, and choosing your gears such that the smaller gears are completely contained within the tube with little/no pocketing required above them.