set an element with `Modal.setAppElement(el) to element in virtual dom

I don't want to attach this to an element that exists on in the html.  I want to attach it to a div that is being created in a render (we are using react grid layout).  The message is saying that the element does not exist and when I look at the console it is true, it does not.  

How do I make this wait until the component is actually rendered?
