BB.... Great helmet!! Did you use just the straight Dremal as is with just the attachment bits or did you use a flex shaft adaptor and bits on your inside the visor area?
I tried using my Dremal plain with just the bits and it was almost impossibly it get inside of my mystery helmet, I then used my flex shaft adaptor and it made all the difference in the world, I was able to get in tight around the inside visor area and sand it all to a smooth an even thickness, using the Dremal sanding tubes, and I used no Bondo or putty what so ever.
Just a thought, I plan on doing that when my new helmet arrives as well.