No supports needed for bottom and cover part. Pocket for dice image insert is printed fine using bridging.
Print bottom part and cover using M601 command in your slicer for pause print and insert magnets. Command should be set for the layer that first covers the magnet, see image. When print is paused insert 4 magnets and continue.
Print 2 pieces of insert part and use glue to fix them in position.
If you do not have magnets you can print parts without it and use some rubber band to hold it together.
If there is a small gap between the bottom part and the cover use fine sandpaper to clean edges and surfaces.