Latenitenate

If I get this 96 Cherokee 2 door (which I probably will-the owner needs to get the battery charged up though and hasn't been really good about getting back to me) I'm going to be looking at fabricating a roof rack that can also hold a yakima kayak holder without modifications. I need to get the dimensions of the clips for those, but do any of you have links to anything that would work well that won't affect gas mileage too much? I'm not sure if I want a spare tire carrier or just a more streamlined rack. I know the cargo type rack would be more useful, but how much do these kill mileage? Considering the boxy body style as it is, I'm doubting it's very noticeable.

Any input is appreciated!

-Nate