I have 3D printed this knight

[![enter image description here](https://i.stack.imgur.com/4hPyA.jpg)](https://i.stack.imgur.com/4hPyA.jpg)

(<https://imgur.com/JAk9JUj>) (source: [thingiverse](https://www.thingiverse.com/thing:2581791)), and I wish to make a box for it. I would like to mold the bottom surfaces of the knight so that it would fit neatly into place, while leaving blank space above so that the figure can be inserted down into the box.

I'm new to Blender (and modeling in general), so my first thought was to slightly enlarge the knight mesh and then apply the Boolean difference modifier on a cube. However this would not allow for the knight to be dropped into place.

How would I make this?