Shao,
I wouldnt use steel at all...even with a paint job itll still rust eventually,not to mention its way too heavy.
Try aluminum, you can get square tubing aswell.
It is easy to cut, drill and rivet too.
I built mine out of it and it wasnt too bad at all, just 3x more expensive than steel, but 3x lighter.
If your ever into a trip out this way again, i would show you how i did mine....Its road trip time anyways isnt it ?
Marc.