Ok, Here is where I did the spray foam. If I had had this at the start, I would have filled the horns first and stuff, but that's ok. Coat the sides, and don't be afraid to coat that sucker, you will be cutting it back after. Then put some duct tape across the gap to make sure it doesn't warp the helmet as it dries. Spray a little water on it to speed it up if you want. Once it's dry, use a dremel with a cutting but and even out the foam. Make sure it sits nice on your head. Sand it out and cover the entire interior with duct tape, paper-mache, and spackle. It get's a bit old, I know.