Thanks for the feedback! It hasn't occurred to me to offset the motors to make it easier to remove the gearbox and give room for the wires. Thanks. As far as how the bottom tubes are attached, they are riveted onto small plates with tabs that fit into small notches in the larger side plates. These small plates are installed during the assembly of the module.
Here's a closer look:
https://drive.google.com/file/d/0B8z...ew?usp=sharing