I'm thinking about getting a MPAC Springtail rack for my back door but I have 2 questions. I'm a little OCD about things rattling in my car, anyone have any problems with them rattling too much? second, what do these mount to? Is it only to the plastic skin of the door or do you drill into the metal? I'm worried that over the years it will get looser if it only mounts to the plastic. Thanks