I poured some phosphoric acid in there (just into the bottm of door at seam), got in there with a brush. Let it dry, then used a good rust prevent primer then a bit of rust proof over top. Now as I gaze at the insides of my door I ask myself "will water puddle? it does not look so smooth!" Am I reading into this too much? Leave it alone? Or, get some self levelling urathane or something and run a bead in the bottom. Put over what I did? Or get in there with a wire brush and clean up my mess?
use por 15 do a couple coats fo that and you will be all set. tape the drain holes so you don't make a mess. Bob