I didn't have any "fire helmet" chaffing problems on my Appalachian Trail thru-hike, but I did need to use Body Glide on my inner thighs for my nuts chaffing. Some people swore by Gold Bond Powder (powdering their donuts), but I found that heals the skin into callouses, not what you want on your sack.... Anyway, I didn't have any problems with my fire helmet, but I do know that Body Glide works well on areas of skin nearby.

Andrew.