I followed you advice and did the about the same thing. The only thing I did different is the mounting.
Did not drill any holes. Plan was to use turn clips, but have found a few pieces of blue painters tape works well. I change them out about twice during their use to make sure they don't stick to well. Just put it over the crack to the window frame, not the wall as the tape could peel off the coating.
Definitely worth the effort. Not only does it cut down on the cold draft, but it also greatly reduces any condensation on the windows.