My SMB came with window inserts for the Barn Doors on the side and at the rear. They would constantly fall out when I shut the doors. They fit perfectly but the momentum of the door closing would pop them off. The inserts are made with Reflectix on the outside and sewn to an inside of the fabric and binding material used throughout the van.
I bought some grommets like this
from the local hardware store and set them in the center of the window insert panel.
Then I took some suction cups
that I bought here
http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1
and removed the split ring. I then inserted the non-suction end of the suction cup through the grommet and reinstalled the split ring to both hold the cup in place and act as a handle to remove the suction cup when installed on the window.
Then I just inserted the panels into the windows and pressed the suction cups to the window and they work great!
From the Outside
From the Inside
Sorry the last two are sideways... you get the idea.
Then when I want to remove the panels I just grab the ring and gently pull till the suction cup releases.