From the designer:

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.

I have also designed it so you can pick between having M18 battery storage or another storage tub. There is a file included for a tub that will sit in that opening as seen in the images above.

The specific M18 Heat Gun that this is designed for is model M18BHG-0, link is provide here: https://www.milwaukeetool.com.au/power-tools/speciality-tools/heat-tools/M18BHG-0.html

We now offer latches to identify which tool is in which case.  Latches are offered at a discount if purchased with a matching insert and are sold by the pair. Please ignore the mismatched latch picture.  If you order latches with this insert, they will say M18 HEAT GUN