I reinforced mine yesterday. I used the Bondo Fiberglass repair kit and bought some extra fiberglass strip. Glad I did - the strips was a little easier to work with and I didn't have to worry about running out.
I have to admit, I was really stressed about this but it went okay. A little of the liquid got on the outside in spots that I assume I can sand off.
Question for those have done this: How long does the inside of the helmet smell? Do you then paint or coat the inside so it isn't as intense? Right now I think I could only wear it as long as I could hold my breath...