Once the primer had cured, I TIG-welded the door bottom (I was skeptical of doing oxy-acetylene again). There was still warping, but it was still easier to planish than MIG welds. I -think- I get less warp with MIG, but I might be fooling myself - there might just be more finishing with MIG than TIG, but I'm trying different approaches to see which one I like better.
Then a good scuff on the inside of the door bottom as well as the skin, and two coats of epoxy primer.
