The GEMMA is housed in the flir-handle-btm.stl with the USB port facing the bottom. This allows you to easily reprogram the GEMMA without having to disassemble the handle.
The 3X AAA Battery holder fits in the large space just above the GEMMA. You may need to secure it into place with double sided foam tape or any other plastic-friendly adhesive.
The slide switch adapter is held in place between the two handle pieces. The opening is located in the upper back of the handle parts.
The MLX90614 temperature sensor is housed in the upper front of the handle and also held in place by the two handle parts.