Well, I changed my mind again. Was all set to add watermelon juice directly to the primary, then I decided I wanted to harvest the yeast. Thought it might be better if I got it before the watermelon.
So I added 8 cups of juice to a 6 gal Better Bottle and racked on top. Glad I added a blowoff tube
So I can't add to list of people successfully adding the juice directly to primary.