John and Andy-
I just finished doing this a couple of weeks ago. I have quite a few pics of the process, but not enough to do a serious tech article. Basically, the bottom 6-7 inches of my front door posts on both driver and passneger sides were shot, this had spread onto the kick panel overlap and onto the inner rocker. Keep in mind this was very isolated to this one overlapping area, which resulted from floor pan overlays placed on the angled part of the floor pan as it transitions from foot bed to firewall. The holes that were underneath allowed moisture into and underneath this area...it evaporated along the tunnel ( no rust problems there and was able to condense and sit on the kick panel. Over time, the kick panel corroded and allowed the moisture to seep down around the rocker and the door post, hence the isolated problem.
What I did was cut the door post about 8-9 inches up, just below the hinge plate retainer and removed the outer section of the door post, then about 1.5 inches below cut that section out. I also cut the kick panel from about the circle shaped hole for the vents to about where the back edge of the floor support meets the kick panel. I used 16 guage sheet to reproduce the kick panel and rocker sections, then spot and seam welded them, reattached them to the floor support (all after the floorboards were removed). Then I made replacement door post pieces, which was quite hard (first timer). I used c-clamps, 1/2 plate, 1/8 inch plate and body hammers to bend shape and manipulate these pieces (A vise, brake or other steel fab equipment would have made it alot easier.) to make pretty reasonable replicas of the door post halves. It actually turned out pretty nice and all the steel is new. I have alot of pics of this process and will have even more of other updates after I get back from having my frame dipped that I can post next week. Its do-able, however. It took me alot of time to do it this way. I could just have easily replaced the door post and inner rocker in less time. It was cheaper and I learned alot this way. Time will tell how well she will hold up. So far, all my friends have said that it turned out really nice and they will usually give me a hard time if they can...I even got a "good job, John, good for you" from one or two. Hopefully, the line-X will buy me a little extra protection. Good luck with whatever you decide John. The toughest part was trying to weld the 16 guage pieces I made and the older 20 guage original pieces...although some of the original steel is 16 guage. I had more than a couple of blow-throughs, but it all turned out OK. Again, take your time, try it with some sheet, if it doesnt turn out OK, buy the replacement pieces, you will only be out time, and $10 in 16 guage sheet rather than the $500 for new panels.