I had someone make a request to design a holder for the Milwaukee M12 rocket light that would mount to the Packout boxes and this is what I came up with. It clamps onto the rail using 4 M5 bolts (I used M5 x 16, but other lengths might work also) so you don't have to remove the rail or leave any marks on the rails either.

I designed this to hold the light with a battery installed so it can be used from the mount and doesn't need to be taken out if you don't want to. I also made a cut out in the back so you can plug it in with an extension cord without taking it out as well. It has a drain hole in the bottom so if any dirt gets into the mount it should be easy to wash out.

In the third picture I have the boxes angled back at about 45 degrees and the light is staying in. I also decided to push it even further and in the last picture I have the boxes almost laying almost flat and the light still isn't coming out. Wrapping Velcro or some time of bungee cord around another rail higher up probably wouldn't be a bad idea though for day to day use just to be safe.