The main body requires supports (for the face where the antenna connector is mounted, because it will face down).
The main body is to be printed with the main access hole up (USB hole on the print bed).
Screw hole is for M2, with heat insert, but it is optional, since the back cap is press-fit-ish.
Pics show 0.2 mm nozzle with 0.08 mm layer height and speeds 50mm/s -ish (over 7h print time, both parts on bed at the same time).
Care must be taken with the buttons, as they can (WILL) break if pushed when board not present inside.
The 18650 cell used was recovered from an e-ciggarette (lilfiit ?) and already had the protection board on it. All that was needed was to solder the 2 wires to the board.
I don't recommend using cells without protection (OVP, UVP, thermal). In the main body  there is room so an external cell protection board can be fitted, but take care to isolate it from the heltech. 
This case design does not provide any contacts to the 18650 cell.
Never solder wires to the cells directly!