I have built a few rods with brackets welded to the rear axle tubes, and have never had a problem with warped housings. I believe that the secret to doing this is to design the axle bracket as a full 360 degree style, that goes all the way around the axle tube. And no, I don't take the rear axle apart to slide them over the tubes---I just cut the bracket into 2 peices, slide the 2 peices over the tube from each side, and tack them back together. I then position them correctly for pinion angle, etcetera, and tack them into position. Then pull the axle assembly out of the chassis, stand it on end, crank up the welder, and go. I start in one spot, and weld about 1/4 of the full diameter, then immediately jump over to the other side of the axle tube and weld 1/4 of the full diameter directly accross from the first weld. Let it cool for a half hour, then repeat on the two remaining unwelded quarters. My theory is this---when you heat the axle tube in one spot, it expands, and then when it cools, it shrinks, but it always shrinks a bit more than it was before any welding started.---this is what causes the tube to bend----If you can weld on two opposite sides of the tube almost at the same time, (as in no "wait time" between opposing welds), the shrinkage factor will now be more or less evenly distributed about the centerline, and will effectively cancel each other out.----after the welds are completed fully around the axle tube, weld the 2 halves of the bracket (which were previously tacked together) solid ------Thats why you need a full 360 degree bracket.---I believe that its all about even heat distribution.