I worked on the sliders this weekend, I went with 2" square .125 tubing for the rails and legs, 1 1/2" square .125 to connect the rails, and 1/4" plate to bolt to the frame with grade 8 hardware. I used factory holes on the frame and think it is plenty strong enough since I am not planning any rock crawling adventures. They provide a nice step for the kiddos have better clearance than the factory steps and should also give nice side protection. It ended up costing around $300 with the metal, cutting wheels and welding wire. It was all done with my Century 80 wire welder that gave good penetration. This project gave me a good opportunity to improve my welding ability, not much grinding needed.
Sorry the pics are bad it has been raining outside, I will upload better ones when the weather clears.
Here is a pic with the legs attached and most welding complete. Then with the rear door open, drivers door open, a full side view, the brackets underneath, and plate on backside of frame