One thing that may not be noticed as to the "why" of doing something a certain way. The crossmember is made from 2 pieces of 1" x 2" x .120 wall rectangular tube. There are 2 reasons, the first is to get enough width for the recessed pieces of tube in them and not have the tubes contact the sides. The second is by using 2 tubes, I get 4 vertical walls to add a bit more stiffness.