The previous owner of my car put them in that exact location. They held well for the first six years of my ownership, and then the screws loosened up and they pulled out. I put some hollow anchors in there and it firmed right up.

The only issue is if you tire of it being there, you will have permanent holes in your door leather.

If I could ask where did you get that cupholder?

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1993 300E
1999 E320 Estate