As I like to explain, from my own viewpoint, WPAD is the very last step in term of configuration.
you have to ensure that your proxy works when explicitly configured on your browser
once this works, you deploy proxy.pac on some web server and ensure it works when manually configured browser side
once and only once this works too, you can push WPAD using DNS, DHCP or whatever supported method.
Following this approach, you may discover that WPAD step is the easiest one and most of the time, it works ;)