It all depends...on what you want to carry.  I have a 4 sets of Yakima
"wide body"s installed.  These are artificial rain gutters of a sort.
With a rack installed you can still muscle up the upstairs bedroom.

Since the devices operate in shear on the top and each has four 1/4-20   
carriage bolts for attachment they'll hold quite a bit.  (5 bicycles f'rinstance)

I also mount a Thule 250 Ski Box which has up to 100 lbs of assorted skis, boots,
poles, czechs etc inside.  No problems yet.  

The devices this fellow wants are Yakima Tall Towers or Terzo Tall Towers which
will clear the top but barely.  You will not be able to pop up though.  The 

Now that I check the Yakalog they're called 1A Hi Rise Towers (0104).  They're
on page 30 of the way spif Yakalog whose Phone is listed as 707.826.8000.

If he's local, I have a set of four he may try at no cost of course but he'll need
66 inch bars or so to span the top floor.

alf@hpptc44.rose.hp.com