Thanks for all the replies.
Rilot - It wasn't until I saw your post that I realized I was overcomplicating things. I attached the case to the DJI stock mount. Thanks.
It's there any REASONABLE way of mounting the gopro in it's protective case under the phantom? I am having an irrational fear of placing the hero 3 in the phantom mount unprotected. Thanks in advance for any insight you can provide.