You say you're getting an awning as well. You may want to contact 1der here on the forum as he sells the preferred mounting brackets for awnings.
Also, mounting a rack to a penthouse top will be pretty difficult to do without the proper "tools". Mounting the Aluminess rack on my van's gutter rails was a bit of a task involving tying it up to a roll up door, someone lowering it into the van while 2 other people balance it. I couldn't imagine having to deal with marking holes to drill then installing on a penthouse top. In short, I guess I'm saying you might want to order and have the install done at whichever shop you order from to save yourself the hassle. It would be money well spent.
2005 E350 Chateau - V10 - Agile Offroad 4x4
2012 CTS-V Wagon - For the baby...