Another way to make sure it's square is to measure diagnally from corner to corner. When both measurements are exactly the same, it's square.
Are you going to weld it all the way around? I'm just curios about moisture and keeping it out.
It probably doesn't compare, but I just bought a stick of 2x4 tubing with 1/4 inch walls for $100. What does it go for in your area?
Eddie
