https://lorraine.mcunderwood.org/raspberry-pi-intercom-system/
3 x Pi's: 1 server+client (Kitchen), 2 x client (Back cabin, Barry bedroom)
Something like this for the actual hardware encapsulation:
https://github.com/dchote/talkiepi
https://www.myminifactory.com/object/3d-print-nintendo-switch-adjustable-stand-with-vent-holes-115735