When using packer to create a virtual box centos 7 VM does packer take care of installing the guest additions?
I have looked at several examples and one of them does the guest additions mounting and installing in the packer json file, is this necessary?
When I run the build I can see that packer takes care of downloading the guest additions but I am unsure if it installs them.
It doesn't install them. That you need to take care of yourself. It will download them to the host and upload it to the guest or attach it as CD.