This is a desiccant box for the quite common 4L cereal boxes sold under different names.
I couldn't find any that really used the shape of the box or was big enough for a decent amount of desiccant. So I made my own.
It uses a nice spot in the boxes, so it's visible from the top and uses a large space without having problems with big 20cm spools. I placed the slits also on the glue side, so people with color indicator desiccant can see the desiccant from top.
It's a 3 part design, so it can be printed without any supports. There is quite some bridging, but this never was a problem, even with earlier test prints. Front and back have angles that help to adjust the parts. Just put some super glue on the rims and press them together and hold for a while. The top will just slide in. It is quite a tight fit, but it works to slide and since you usually don't change the desiccant that often I wanted to make a tighter fit.
I uploaded 2 versions. One version where the slits are all around the parts and also one version with a solid face on the back. I think this is usefull if you want to put a Label there or write something with a marker.
One tip: It's actually really hard to glue something to PP, which is the material of these cereal boxes. You need a special glue for that or (although not that pretty maybe) just use heat glue sticks. Super glue will not work with PP.