Jango's gun belt attaches to the codpiece using a custom bracket that isn't included with most armor kits.
This is my take on how to handle that part of things. I recommend printing it on its side, so that the strength of the layer lines is in your favor. Do 3 perimeters on a 0.4mm nozzle and it should print out solid. You'll need supports for the weird overhangs, but it's worth it.