You need to remember there is literally no way to keep water from running down in the door. The rubbers are designed to "slow" the amount of water that gets down there but with any car, even up to 2012 there is no car that has a moving window that doesn't have some water get in there, that is why the moister shields are behind the door panels, because SOME water is GOING to get in there. Every single car has a little water get in, so every single car has drain holes where the water gets out. Some have little "valves" a rubber flap so the water can get out with nothing going back in. But they ALL have a drain at the bottom for the water to get out.
As mentioned in the previous post you need to think more about cleaning up the inside of the door of rust and debris and epoxy prime it, and clear out the drains. You could also seam seal it at the bottom LEAVING the drain holes open of course so the water doesn't get into the seam. But usually liberally applying epoxy primer will also do that.
And by the way, many early cars that Chevy being one of them have a sound deadening material stuck to the inside skin, a felt or tar sheet that is glued to the skin. I have seen these retain water where the panel rusted out right in the middle of the door! This is very uncommon as they will rust out at the bottom where the inner shell meets the skin a million to one in the middle of the door being there is nothing to trap the moisture up in the middle of the door.....except for that darn sound deadening material.
So think about removing it too and replacing it with some spray in once you get that metal nice and clean and epoxy primed.