I got the Arkon vent mount for my XL350 yesterday. Now, I no longer have to worry about the suction cup coming loose. This is a good product at a great price:
Amazon.com: Arkon TTEP129-SRVC TomTom EasyPort Mount - Removable Swivel Air Vent Mount: Electronics
Amazon.com: Arkon TTEP129-SRVC TomTom EasyPort Mount - Removable Swivel Air Vent Mount: Electronics