You might try the Eastwood PDR system of dent removal.
I'm not sure if it will stick to the grain surface.
Do note that although I've had success with the Bondo method, it requires a great deal of experimentation. It is extremely finicky about timing, latex prep and mold removal liquids to get right.
If you do not have great patience, don't even start. And you would need a spare door.
If you can actually reach behind the panel after gutting the door judicious use of a small, lightweight body hammer and dolly does work. Body hammers should be used with a light touch and many small blows to slowly work the dent out.