I propose the use of a dedicated package building system for Whonix project packages. The most advanced one I have found is the Suse developed Open Build System. Most important features are : Supports a wide variety of distros and package formats. Can fetch from different collaborative coding platforms including Git. Supports different hardware architectures (think ARM support). Supports reproducible builds.
Besides being available as an online service, the build server software is available as an appliance package you can download and use locally. 
Open Build System is used by some major projects: Linux foundation and Tizen. 
The Open Build Service (OBS) is a generic system to build and distribute binary packages from sources in an automatic, consistent and reproducible way. You can release packages as well as updates, add-ons, appliances and entire distributions for a wide range of operating systems and hardware architectures.