To get the same durability the aluminum will have to be thicker and the weight will go up. Being thicker it will be more difficult to bend. Also welding aluminum requires more expensive gear than steel and that will drive up the cost. This is a case where steel is probably the best choice.

ChuckH, what happens when your design bends? Will your reinforcement ribs impact on any of the delicate bits under the body? Overall I say good job. That's good work even if the welds don't look absolutely fuckin' perfect. Speeking from my experience, I would crush them at some point.

I have a SR skid that is bent to the point it's resting on the transmission. Whenever I come to a stop in Drive it rattles pretty badly. I wish there were more reinforcement in the middle of the skids.