I used Oxy/Acet to braze the rocker in. Plugs on the bottom, and seam on the rest. The forward part of the rocker was seam welded over the kick panel. I used one of those to spot weld drills and a cut off wheel to remove the panel. I have since used the spot weld drill only where I cannot get a grinder to.
The hardest part (aside from not burning the fuzzy seals) was getting the replacement rocker into shape. The parts we get now are in the general shape of the original. It took a lot of metal pounding, shrinking, tuck shrinking, cutting, and stretching. (I ruined my first rocker) Fitting and refitting to get it right. When done, it should fit without forcing. Also, you must have the doors on to check the fit as well as the fenders. I must have put on and taken off the fenders 100 times.
The rocker provides a lot of support for the "A" post. You will be surprised how much the forward door post moves around. One of several mistakes I made was to not support it well.
While many feel the greatest challenge is the welding, it's not. You can braze, MIG, TIG, and or spot weld. It really does not matter. The BIGGEST challenge is to get the rocker into the proper shape and fit. Before you jump into the project take a good long look at the replacement part and the one on your car. Then decide if you have, or are willing to learn the skills needed to shape the part.