I have found the dimensions for the box in the datasheet. However it is not very specific on the usable space on the inside / it doesnt specify the how much the screw terminals or the middle rods come out. Since I do not have this box, can somebody please roughly measure these dimensions for me? 
What exactly do you mean by this? Could you please explain what do you mean by “middle rods”
btw sorry for the late answer.
Never mind: I do have my own box here now and can measure it.
The idea behind this that I wanted to manufacture a fitting PCB so there is enough space left. I came to the conclusion that it makes sense to mount the electronics as high as possible to be safe, as was proposed by someone here. For now i manufactured my rectangle PCB. However it will be tighter to fit since its bigger than the previous two single (PSU/Arduino) boards.
nice! But is better to have all electronics higher than the axis mast in case of leak.