I have a 36 inch prehung entry door that sits on a sloped (pitched) concrete floor. The gap under the aluminum threshold is 3/4 inch to nothing, has a 3/4 inch shim on one side and the void is filled with expanding foam. Lately , I've been having water coming in under the door. I'm planning on installing a new door and I would like to know how to go about this the best possible way?