This is just a short update to show the result of added panels. I removed the additional supporting beams which were used to mount the USB hub and Up board. Instead these will be mounted on the panels saving some space. Although the idea is to add a fleece skin to the robot, the panels provide protection for the electronics and make for a more generic base.
The panels are made from the same 8mm polyethylene as used before (a.k.a. Ikea chopping board). The panels slide in the slots with M4 bolts. The other sides have 5mm rods which provide additional support.