For people who have been around Cherokees for a while,what I am talking about is probably old news...But for those who are newer to Jeeps ,or about to buy one ,this might be of interest.
I have been surprised about the amount of rust on the right side floorboards. Left side is almost perfect... I got the Jeep up on jacks today and I was rolling around on my creeper. And as I was looking at the
holes that had rot that I cut out, it was all above the exhaust pipe. So I am guessing the heat compromised the paint. Allowing rust an easier route ....
So ..If you are buying a Jeep and are at all concerned about floor rot, I would think the right side is the 1st place to look. IMHO

 

Usually more water leaks on that side too. Then the carpet holds it and makes even more rust.

 

As some know I am actually fixing this very area right now on my 93.
Besides the heater core leaking, I noticed that there are water flow marks on the firewall pad around the heater / AC line entry seal.
My seal looked like Swiss cheese when I first got my Cherokee.

Instead of the factory seal, I am trying to come up with something more substantial that wont break down as fast as the foam that is subjected to Heat, Oil, Water, and what ever else leaks in the engine compartment.
HEY IT"S A JEEP!
It was designed to leak somewhere?

 

I got lucky with mine because the underbody is in good condition. The only thing that has me concerned is the rear shackles but my shop says they're fine... for now. I know by the end of next winter I'm going to have to do some major rust repair because of the shackle rust and the driver's side rocker panel has a quarter sized hole in it. I've got some body holes to fix but a grinder, sheetmetal and an hour of time will solve that.

 

I had rust in the same spot on the passenger side front. It was definitely rusting from the inside out. So took a hose to the outside and found out the rubber grommet that holds the antenna wire through the inner fender was not in the hole. Fixed it and sealed it. Golden. The little things in life...

 

My passenger side is in pretty good shape but my driver's side is better. My little theory is that all the crap on the roads (whether it be water, salt, etc) ends up in the side of the road. Where your passenger side gets exposed to more of this crap then the drive's side.

 

Well, the shakles will be fairly easy....once you get them out.

I've noticed this in pretty much every vehicle I've worked on as well, and I agree with your theory. I also agree that the heat from the exhaust takes its toll on the passenger side of an XJ. I've noticed the paint under mine has turned a gray, carbon-y color above my cat. converter like it's slowly burning.