I have the first set of 4-door sidekick sliders that he made. They've taken a huge beating and are still straight. The mounting points have bent just a fraction, but that's most likely due to the fact that mine were prototypes. Since then, he adds gussets to the mounting points (i'm talking where it slides over the frame and bolts on) to stop anything from moving. The only thing that happened by them moving a fraction is that they're now closer to the body, but they're still straight as an arrow. He uses square hitch tubing (thick walled) and I'm not sure what round tube, but it's ultra tough too.
Worth the money and the 30 mins to install.