Finished. I see nothing but flaws when I look at the paint, of course...but it looks pretty good from 20 feet away. Since the van itself is a solid 50-footer that works.
I'm impressed by how sturdy it ended up. I can grab the rack and rock the van side to side with it and it doesn't flex or shift.
After a bit of struggling, I realized the trick to getting the mounts to fit properly in the rain gutters was to position it with everything loose, clamp the mounts in place, then finally tighten the bolts between the mounts and the rack.
Took the van for a drive to see if the rack was noisy. It isn't to a degree I can detect in an admittedly already noisy van. Unexpectedly, it seems to have altered the airflow over the roof in a way that causes the roof to surge against its hold-down clamps a lot less, so it actually has made the van *quieter* overall. Go figure.