Hey Don---unless you plan on using plate 1/4" thick, or thicker, forget about it spreading the load. Plate has very little or no resistance to bending in the "flat". When I went down to the steel yard today, they had no rectangular tubing, but did have a whole bunch of 2" x 1" x 3/16" channel. I am using the channel to beef up the pressed steel runningboard supports, and I am going to weld one peice of channel between the front and rear supports with the toes pointed upward to straddle each side of the ridge that runs up the underside of my glass runningboards. This will definately have superb resistance to bending and will spread that load carrying capacity over the full length of the runningboard and tie it into the beefed up supports which carry back to the frame.-----as the old farmer said "Hell son, you'd be able to bull a cow up there ifn you could get the cow to stand".