Observe the image of my car. The black plastic line on the side, is a dent protector. I even deliberately tried to make a dent with a number of cars, to check how effective it is and it even worked against an SUV. Any door will hit that plastic before it hits the metal.
Just a suggestion, maybe you can put something on that works the same way
Oh, one more thing. Any dents visible on this image are because of impacts with local flora and fauna