You will want to remove the trim that covers the bottom of the exterire door also. Bottom of my SD doors had surface rust that was easily treated woth POR. Ignoring would lead to replacing door or metal.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.