the door seal is pretty much irrelevant in keeping water out. you need to make sure the ground is graded away from the building to keep water from getting close. If the floor is lower than surrouning, you're pooched. a sill beam can be added for the door to mate to, and give you some added inches to dam the water out. Think of a speed bump (or speed hump for Evolver) right across the threshold.

and x another one on overhead door. they're even big up here!