Modify Device Casing for Slide-in Rails

I need a plastic device casing modified in FreeCAD. The top and bottom parts should be assembled via a single rail on each side instead of pilons.

Requirements:
- Use FreeCAD for modifications
- Implement a single rail on each side for assembly

Ideal Skills & Experience:
- Proficiency in FreeCAD
- Experience with plastic casing design
- Familiarity with slide-in rail mechanisms