This is the kind of Velcro used to attach the support to the car. It's specifically for heavy items.
We will paste two, one for the iPhone in the vertical position and one for the horizontal position. Before placing them check their position and adapt it for your car.
This way, you only need to use one piece of Velcro on the car.
(more information at http://www.estudidisseny.com/iphonecar/