I've been driving Cherokees ever since 1987. When I bought my 1987 Jeep I also bought a roof rack system called "Quick N Easy". They clamp onto the roof gutter rail and you supply your own 2"x4" wooden cross member and hardware. When I bought a 1996 Cherokee and I just moved the rack over to the new Jeep with no adjustments needed. The whole thing was really cheap too. Since gutter rails on cars have gone out of style, I doubt Quick N Easys are still available. I've hauled 2 canoes on it at the same time, 60# & 80#.
On another car, I've hauled canoes on the factory installed roof rack... the kind of rack thats supposed to haul luggage and other light stuff. To keep the light duty cross-over rail from flexing too much, I inserted a small, 12" block of wood between the rail and the roof, right in the center. I cushioned the wood/car contact with a piece of bath towel.