| I've been cartopping a Wave on my F-150.  It's not a Passat, but the principle is the same.  I use a Yakima setup, with rack pads under the hulls, and tie-down straps along with bow and stern lines to the front and rear of the truck.  The masts are carried on the Yakimas also, using Multi-Mounts (2 pair).  Setting up the Wave takes from 15 minutes to 1/2 hour, depending on experience and motivation, assuming 2 people are doing it.  By yourself, it's do-able but a real pain, and not something you would want to do often.  I would not recommend a larger craft. 
 
 |