Boxing in frame

I went to a rock garden today and bashed my "frame" rails a little. I've read in the past about people boxing in the rails, after seeing how easily that metal bends, I want to know how to box them in. How do you weld the angle iron on? Just at the top to the floor, or directly to the "frame" rails also? Does boxing them in stiffen up the chassis at the same time? What thickness of metal have you guys used? Thanks in advance for any info.

3" x 3" x 3/16" angle iron seems to work well for GaryE, and he swears the chassis is much stiffer now. Weld them to the outsid of the "frame" rails, but be sure to grind all the undercoating, paint, and galvanizing off before burning any wire. It contaminates the welds to no end if you don't.

CRASH

I did it mostly to protect the framerails from extra denting, and to provide a foundation for long arms and a traction bar. I don't know how much it stiffened but I seem to notice less squeaks and rattles. Essentually its the same thing as the t and j chassis stiffeners just much cheaper.

I did it with 3x3x1/4 angle and bolted it to the unibody. Drilled holes every 12 inches and bolted it up. Seems to work good. I also made a new front leaf spring perch on these. Mainly because I tore the old perch off of the truck last year.