Using a WD My Cloud with an Apple Airport Extreme Base station router through OpenDNS

Configure the Airport as you did originally. 

Connect the WD MyCloud

Use an DDSN Service such as  https://www.noip.com

This post may help,  http://community.wd.com/t5/WD-My-Cloud/HOW-TO-Troubleshooting-Remote-Connectivity-Issues/m-p/617261#U617261