The ones I made were all from 1/8" x 2 1/2" cold rolled steel. The rails are 2 1/2" wide so I cut the bottom 1" out of the frame and wire wheeled and cleaned the rust as best I could from the inside. I believe safety caps go up 3" and the rails are 2 1/2 x 4. It is easier to weld with the mig.I never lifted the frame from the body. My centre mount was shot so I made the caps for each side for that also.I will put a pic of them also.
View attachment 58271 View attachment 58272 Depending how far your rails are bad will decide on how long you need to go.If someone is doing it for you you may only have to do the area under the skid. You can see I had to bend the side rails first and c clamp them on the frame. Then I fit the bottom right to were they turn. Then cut the bottom ends to the angles needed. Tack them in place from the bottom well they are clamped on the sides. Then remove the tacked assy from the frame and put a few 2 1/2" spacers of steel tubing inside to keep it spaced. Then fully weld the inside edges. I put drain hole between the nuts I welded in . Before you weld the assy onto the frame you have to reclamp in place ,set the skidplate up and mark were the 6 bolt locations.remove ,drill the holes,weld the nuts in place and then reinstall,bolt the skidplate up and leave in place .Then put some 1/2" welds here and there so you know the skidpate will rebolt up. Drop the skid and fully weld.