[quote="citylights"]Nicely built! Are you going to paint the pipe? You said it was SS, stainless steel? That would be uncommon and expensive pipe! SS would be fine unpainted, but steel or even galvanized steel should be painted. Galvanized should be painted because it galvanization was messed up where it was threaded for the caps.
I like the bolts through the sidewalls. Nice and strong.
I bolted mine through the 2x2 roof spars that were placed specifically for the roof rack. Your vent protection is interesting, I had not thought of that. I made mine so that the vent can only be cracked when loaded on top of the rack. I would need to remove things from the top to open the vent fully. I was trying to keep it as low profile as possible. I also used what was the trailer ramp for the roof rack, so mine is steel, isolated from the aluminum skin by felt pads (bolted through at the bolt points) and all painted black to blend in with the other trim and trailer pieces.
Here is a shot of mine.

No paint on the stainless steel cross pipes, got lucky in the scrap bin at the shop and scored 2 pcs long enough to do the job at hand. My side brackets are 10 ga stainless with 10 ga stainless backing plates and 5/16" stainless button head allen bolts. My vent box was designed with the thought of being able to crack it open a good distance if I should be just spending the night on the road without having to move things around, the punched or perforated metal while mainly protecting the vent will also help dissipate some air I hope. My rack is basically 38" wide X 49" long with 5" deep sides, I could have easily fit a 5 or 6 foot long rack on top but then I would tend to overload it and maybe cause myself some grief.

As it sits I think it could handle 150 pounds or so spread evenly with no issues, but I will never approach that kind of loading.
I fear the day that technology will surpass our human interaction, the world will have a generation of idiot's.