Below is a link to my cup holders.
One problem with putting the cup holder in the door panel is that it is not vertical. Something like a McDonald's or Starbuck cup with a plastic lid will leak on your carpet if full. I have a coffee stain I need to clean. I think something like a CONTIGO cup with auto-lock nondrip should be used. It might have been better to mount them on a vertical surface in front of the door but I would have to enclose them on the other side.