If you would like to use a stable, predictable, manageable and reproducible distribution in your AppVMs, you can install the Gentoo template, provided by Qubes in ready to use binary package. For the minimal and Xfce versions, please see the Minimal TemplateVMs and Xfce TemplateVMs pages.
The standard Gentoo TemplateVM can be installed with the following command in dom0:
[user@dom0 ~]$ sudo qubes-dom0-update --enablerepo=qubes-templates-community qubes-template-gentoo
After a fresh install, we recommend to Update the TemplateVM. We highlight that the template memory/CPU allocation certainly need to be adjusted in some cases. As Gentoo is a linux source distribution, the template needs resources to perform updates or installing any packages. By default, each TemplateVM has 2 VCPUs for 4000 MB Max memory allocated. If needed, double those values, 4 VCPUs for 8000 MB Max memory. For example, it has been observed failing updates or builds with 4 VCPUs for 4000 MB Max memory due to out of memory issue. For more general considerations, we refer to the official Gentoo Handbook.