This is how you build and install the debian package for the gswitch application:
git clone https://github.com/karli-sjoberg/gswitch-deb
sudo dpkg -i *.deb
rm -rf gswitch*
sudo gswitch setup
This package also comes with automatic detection of eGPU at boot!
After gswitch has been configured and you've got the switching set up, simply run 'systemctl enable gswitch' and it will configure the eGPU automatically when you boot. It will also also switch back to internal if you've by accident forgotten to switch back to internal when leaving home and found yourself stuck at a black screen; no more!
Yeah, that happened once too many ;)