Improving the seal from outer firewall to fender on early cars?

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Anyone improved the seal that runs vertically between the front fender and the outer firewall? From the factory it looks like a simple piece of rubber on the backside of the filler panel. This did not keep the dirt out and filler the lower fender with dirt and then it rusts from inside out. Trying to think of a better way but its a poor design to start. Curious if anyone tried something with good results?

Thanks