[B. W.]

Before trying heat, push the low spot out from inside the door using something with soft edges. Use a slapping spoon on the high spots around the perimeter of the low spot. You may be able to remove the oil canning on some or all of you low spots without having to heat.

I'm fighting the same issue on my roof but I can't access the inside. I'm pulling up with a suction cup or using a welded stud then slappin' away. I have had success with a couple of large oil can dents this way. (still have more than a few to go, looks like cows walked on my roof!)