P8, Windows 7.

I'm working on an IDL scene that is too ambitious for my computer so I want to break it down into layers. I don't have postwork software, so my layering is done render on render. Before IDL, I would simply render the background, export it as a jpeg, import that jpeg as a background  and then render the foreground with shadowcatcher enabled. But with IDL and a skydome, that poses a whole new problem because the skydome will block any background picture.  I have an IDL cove (background prop); should I texture the cove with my first render (background)?