A new door should not leak like that! I recently had new doors install in my century home and they all perform beautifully...no frost on fixtures at all and it's been -25C here for a few weeks. There must be something wrong with the install. Putting on a storm door over an insulated door will be a temp fix but doesn't address the original problem of leakage and may cause further problems down the road by trapping warm moist air between the storm and your insulated entry door. Not sure of the fix but that ain't right!