I used the 1" square tubing like the OP, and added an aluminum L bracket on top of it. I used longer bolts to go thru both the L bracket and the square tubing, no welding, but may do that in the future since I have a TIG welder.
I like the extra lateral stability the L bracket provides and I used the wing nuts to make removal quicker/easier. This way I can leave the supports on and take the rack off. I was thinking of maybe putting some cross bars up for mt. bikes, or whatever.
It's not hard, but a little tedious when it comes to lining up all the mounting bolts. By the way I used angled head bolts and countersunk the holes so they are flush.
Hope that helps. Let me know if you want to know what hardware to get, I went to Ace hardware about a hundred times figuring it all out and would happily help you avoid that!