I have some minor light leaks under the door of my darkroom that in almost 20 years of use have never lead to fogging. It takes me a minute or two of complete darkness to see them. However, when loading film onto reels, I don't want to take any chances and either make certain that the "minor" leak is sealed or that it is dark outside of the darkroom.
May that as it be. It is extremely easy to make doors totally light proof. I suggest to stay away from seals of any kind and use a light trap design instead. An extra piece of wood, painted black on the exposed sides does not conflict with the operation of the door but prevents any light to come in.