So the XJ guys do it all the time, mine were gone, so why not try it? I used 12' of 4x3 11ga steel that ran me $60 cash and a few rattle cans of "corrosion resistant" rubberized undercoating. Cut out was really easy because the bottom at the pinch seam was literally 90% gone, the top seemed more solid but that turned out to be not all that true. We had to notch out the tubing in 2 spots where there were structural components. One was at the front of the front door, the other was at the pillar between the doors. There was another brace that appeared to give lateral stiffness to the rocker area, I cut that one out since the box steel has way more strength than the rocker ever had. After the cutting was done we jacked it into place with a slight downward angle and welded the top in place. It was rough welding because the steel was so thin in places. You'd start getting a nice bead and it would blow through. With the top done the pinch seam extended about a 1/2" past the steel, so we hammered it around the bottom of the steel and welded away. I then taped off the door jambs and gave it a couple coats of undercoating. I still have the passenger side to do so I'll try to get some pics of the process. But in the mean time here are a couple of the finished project. It's still a rusty, ugly beast but it's my rusty ugly beast. Probably the best $250 vehicle I've bought.