Delp, I am having a fan installed next week, a MaxxFan 4500K.
The fun thing about the MaxxFan (apart the fact that it is a good brand) is that the sides sit on upper groves, so the lower groves (two of them, I think), will be in front of the fan.
I too worried about the groves, but the guy that's doing the job was almost insulted when I asked him if the installation could be a problem "Sir, I've been doing that for 30 years, I know what I am doing".
Just had a bad experience with a so called pro, but this one I tend to trust him. I wanted an opening window on the side door, but he refused to sell me one. He told me "I could sell you a universal one, but your van is too nice. We'll wait till they come out with a window specifically build for the Promaster".
He is suppose to do the job next week. Lucky guy, you can wait to to see what happens on some else's PM.