Well, I'm not engineer but I consult some of my metal working friends and they give me suggestions and thats about it. I went with 1 1/2 square tube 1/8" wall. I added the angle supports so the 72" long side load was carried better and distributed to the legs. So far there is no bowing at all. After I welded it I stood on one of the sides and bounced on it and there wasn't any deflection so I figured it was good.