I use the Yakima Fake Rain Gutters to attach a rack to the tilt up and
     bicycle rack to the hinge system.

     No problems in <100Kmi hauling all sorts of swill including boats,
     Thule boxes filled with skis, yakbaskets filled with wood, 30Gal of
     water, etc.

     The disadvantage of using tall towers is that one can't open the top
     to enjoy the luxurious accommodations and fine view for which one paid
     so dearly.  They also have an issue regarding lever arm at the gutter.

     The disadvantage of using my technique is that you pretty much have to
     unload all but ~50lbs of the swill in order to activate the
     Tiltin' Hilton.

     Your choice of course.

     Thule makes a set of very tall towers that will clear the roof nicely.

     The Yak extenders almost fit the bill but have a clearance problem
     with the roof.

     Just my 0.03$CDN.

     al