You asked "For people that installed panels like these, what size bar stock did you use to make the cross bars for the panels?"
I used 1.5" x 1.5" x .25" aluminum angle for the framing, purchased (next day delivery) from McMaster-Carr
, which is a great resource. The actual mount of the solar panel to the radar arch was 1.5" x 1.5" x .125" aluminum box channel. You can see the result at my projects page