Or you guys can do what I did and get a large magnet sheet like used on commercial vehicles on the sides of their cars for advertising the same color as your rig. Cut it out so it covers the sunroof and the magnet sticks to the metal roof panel around it and it seals it up.
You can order them on-line or go to your nearest custom sign making shop and they will more than likely have it. Just get one thick enough so it holds tight and won't blow off on the highway.