The project got shelved again because the lion kingdom discovered yet 1 more laptop in a corner of the room.  It's mane use would be an emergency job interview or a radio test.  Otherwise, it's worth zip, but not until after some more notes.

Reusing a 10 year old keyboard would require a 26 pin 1mm pitch FPS connector.  A wireless user interface is highly desirable to reduce the cabling.  There is a very klunky keyboard/trackpad for just making it work:

https://www.amazon.com/gp/product/B07FSKZVRG

It's 1 pound.   Maybe it could be hacked into a more desirable trackpad arrangement.  The raspberry pi & battery could go next to this style keyboard, but the compute module is still going to be a giant brick.  A brick battery is far cheaper than anything flat.  

The enclosure wouldn't bother covering any electronicals except where protection is needed.  Plugging stuff in would entail accessing ports inside the enclosure.

The Dell Griffith Mark 1 shower curtain rings 

https://www.thingiverse.com/thing:5403824

proved an interlocking slider mechanism could work for holding up a folding display.

The battery would use standard RC charging practices.  It would be taken out to be charged & stored in the freezer most of the time.  A diode would switch between manes & battery.  There would have to be a coulomb counter 

https://www.amazon.com/ANKG-Precision-Measurement-Connectors-connected/dp/B07YF393ZH/

& a buck converter to power the keyboard.  An adapter for micro HDMI is already in the apartment.  All this stuff would just be thrown in a big old case next to the keyboard.  It would be as simple & bodged as possible.