The actual holder is pretty simple: a V-shaped structure hold the battery in-between the electronics.

One slot is used for the USB ports (for programming purposes), one switch and two LEDs (power and status) are also planned.

Another disc is snapped in at the bottom.

Didn't take any pics of the printing in progress, but here it is after I started to fit the microcontroller.

The altimeter is also in, along with the radio module!

So far so good, the whole thing fits perfectly in the body tube, along with the batteries!

I still have to put in the SD reader and the step-down regulator.