I used the same material on both of mine. Use it all the time. Powdercoated mine tho.
I built mine as more of a "proof of concept". When i am finished modifying it, I'll pull it and sandblast it and get it powdercoated. Nice job BTW.
Very nice! Any pics on how it attaches to the roof?
I don't have any pictures but basically I welded a collar nut into the end of the "legs" of the rack, drilled holes and ran bolts and washers up from the inside. Before i tightened them down, I sealed around the bolt, under the "leg". I let that skin over and then snugged them up a little more, then when the sealant had cured, I tightened them down.