I called the co. that I bought my new door from. They also installed it. He said a caulk was applied underneath it and there is no chance of the sill warping. I told him I did not like the look of a gap underneath it, and the fact that water will get underneath it when I hose off my deck.
He was super nice, and will be out on Monday to put some concrete, or some type of product underneath it to seal it.
Thanks everyone for your help.
Much appreciated.