To bring life to an old thread
I apologize for the crappiness of the photos...
I have a Columbus tent (Autohome) on Thule bars. I got the bars extra long -- they were the same price, I think, and I figured the extra length would be good for something. Turns out I was right.
I bought some pieces of 6" wide (I think) commercial door step -- the stuff that covers the line where the inside meets the outside under the door of a store or office building -- and used U-bolts to mount it on the thule bars.
They're great for shoes at night and, as an added bonus, makes for a really handy "coffee shelf" to put your cup while you get your keys out and load stuff in the vehicle. (Until, that is, you drive off with your cup still up there.)
Note: ignore the eye-bolts sticking up; I was playing around with the idea of limb risers, but the shelves aren't strong enough.