OK, got these installed this week. Well, I did the front, I still have to go do the back roof.
I figured I would take Cerial's advice, and do the opposite, since that usually works out best. These are from SnoBlox, this is the 'Deuce' model. They are clear, and really disappear into the roof from further back. I don't really care about that one way or the other, but some might. You can see how much they disppear into the first two pics (same pic, just zoomed in a little bit) One every 9", in a staggered row. Installed pretty easy, they are dimpled for drilling, so I predrilled each one, then use a hammer to set the self-drilling screws (monster #14 screws with hex heads) into the steel. The complete bottom is covered in a thick layer of sealant, and it comes up around the screw heads also, which also have a sealing washer. Once I got the rythym down installing them, it went pretty easy. Setting the screws with a hammer helps a lot, and I used an impact driver, compared to a drill. Here's a couple pix.