I picked up this mount not too ling ago. I thought I should share it since it doesn't take and drilling or modifications to install and it's very secure. It mounts to the floor by sliding under a bolt that holds down the passenger seat. The seat slides easily and it has a 15 inch bendable arm.

I've never had a gps signal issue and it's in a great spot to use the Ipod cord that the Mini uses.

Arkon 15-Inch Flexible Seat Bolt Floor Mount for iPhone $22.95(Black)

 

I looked at that, but it seems like, with such a long arm, it would shake quite a bit. Is that a problem?

 

Not at all. It doesn't move. It takes some force to get it to bend.