I use a kayak and Overcamp RTT on a Jeep Wrangler LJ which is about the same size as a Cherokee. A longer kayak than mine would fit just as well.
You probably should use three or four crossbars for the RTT on a Cherokee. The problem here is that the kayak hull is probably not flat so you'd probably need to add something to the front and back crossbars on the kayak side so the boat just rests on them.
Expensive? yes. Worth it? I think so but if I had to pick the RTT or the fridge, I'd take the fridge any time. In fact the Jeep broke down on day one of a three week trip to Newfoundland last year (OPDA broke and killed engine) so we abandoned the Jeep and RTT, rented a pickup and strapped the fridge and cheapo storage into the back of the cab. And slept in a hike tent so small you can't both sit up at the same time and it was fine and we'd do it again in an instant. We also learned some good things about pickup trucks: tailgates and firewood storage!
