@doniks Yeah I already did that. They use a script with vmdebootstrap to build a debian , which is similar to the way the ubuntu-touch image is built. It should probably be possible to modify that script to build ubuntu-touch.
Image build script: https://source.puri.sm/Librem5/image-builder
Flash scripts: https://source.puri.sm/Librem5/librem5-devkit-tools/
The images are a bit different and have the kernel on the image itself and a boot sector from what I can tell.
I currently struggle more with figuring out how the ubuntu-touch image is built. I know the rootstock-ng is used, but I'm not sure what parameters are used on the Jenkins.
@UniSuperBox is there somewhere a list of repositories and packages (meta package or a list?) that are used to build the image? I already asked in the UBports_porting channel but got no answer so far.