I installed solus on VB successfully, however I couldn't install VBoxGuestAdditions.
I found this in the logs
vboxadd.sh: failed: Look at /var/log/vboxadd-install.log to find out what went wrong.
vboxadd.sh: failed: Please check that you have gcc, make, the header files for your Linux kernel and possibly perl installed..
/opt/VBoxGuestAdditions-5.1.4/src/vboxguest-5.1.4/build_in_tmp: line 67: make: command not found