This is the one I use. I like it and it protecs the helmet very well. I usually store it in the bag that came with the helmet inside this case too. No sctrached lenses either. My last helmet looked like it had been in battle so I'm trying to take better care of my new Bandit.
When I was on active duty we all used them to carry stuff in everyday. They are well built and take a beating. We called them CVC bags. Combat Vehicle Crewman helmet Bag. You might be able to pick them up cheaper at a Army Surplus store or check out