Elmer's glue pancakes out and loses its bulk as it dries, making it less than ideal for filling gaps, especially large ones. And if the space is too big, the middle will be airtight and will stay wet. If you're willing to put on a few layers, it should work, but try to get Elmer's GlueAll rather than their watered down School a Glue or the fast setting, high shrinkage Carpenters Glue.
How big is the area you're trying to fill? Have you considered air dry clay or automotive Bondo?