This is a custom insert that I have designed to fit your Milwaukee Packout to store your M18 Heat Gun and accompanying kit. It specifically fits the Milwaukee 48228435 PACKOUT Compact Organiser.
The specific M18 Heat Gun that this is designed for is model M18BHG-0 as below:
https://www.milwaukeetool.com.au/power-tools/speciality-tools/heat-tools/M18BHG-0.html