We purchased aluminum "sign metal", which is painted white on both sides. . . we're thinking it was .070-.080, but we can't remember for sure
. We had it cut to the correct size, and since our MCI-9 had trim pieces between each window, we were able to do ours in sections, one window at a time.
We used "Closed end" rivets. . .which are good for structural strength, we used 1/4" for the verticle posts, so you have to have a heavier duty pop rivet gun. These type of rivets are more waterproof because the center doesn't pop out. Ours were aluminum. We glued a strip of rubber shower pan liner on each post, so that the metal was against the rubber instead of metal against metal. Then, we drilled out all the rivets along the top above the window, put a piece of ducttape on the back of the sheet aluminum along the top (again to keep metal from touching metal), and slid it up under the lip from the roof metal. I also made sure I used a very good caulk called, "Through the roof", which is about $4.50 a tube, but really good. It's really sticky, and takes a while to set up, but it sure is good stuff. I put a bead of it on top of the rubber strip on the verticle post, so it also helped seal the holes where the rivets when through.
One thing we did that really made a difference, in our opinion was that we mounted the metal during hot weather, but then also ran a kerosene bullet heater on the inside of the bus, aimed at each panel, as we mounted the sheets. We kept the metal hot enough that you really didn't want to leave your hand on it for very long. This way, we got a really smooth look. Talk about hot. . it was about 95 degrees outside and I swear, in there where I was perched, it was probably 140 degrees! And then, add in the stupid black sticky stuff that I managed to get smeared all over me. . . it was a real hoot! ha ha However, no matter what the temperature is outside, the metal is straight and smooth! YeeHaw!
One of the other things to do is, he cut all the extra posts (two per window) and drilled all the holes for the rivets all the way through the post on his drill press. That way, after they were welded in place, I drilled from the inside out, to make a corresponding hole in the metal, then he stuck in the pop rivet and tightened it. I believe our rivets were like 3" apart or so. By measuring and drilling all of the posts identical, the rivets are in a nice neat line.
I can send you a few pics if you'd like. Christy