I have experience in creating GUI installer on Mac.
If I am correct, your qt project can already run on Mac.
You want to have an installer for your application that can be added to your build process seamlessly.
So basically, what i will do is to depending on your existing project structure, add an extra build step to package your application.
Then I will document the steps you need to take to build your project as well as help you understand how you might modify it in the future.
Contact me and discuss if I misunderstood your needs or you have any questions.