I use moth balls as well. I usually just sprinkle a box of them all the way around the outside of the car on the ground. Never have any probs.when i store my car during winter i place moth balls in small pie pans in various places (trunk,under front seat,on air cleaner)through the car to keep the rodents out,also place pie pans with charcoal beside the moth balls to draw the moisture out of the air.read about this years ago in some car magzine and it seems to work.
I know charcoal absorbs scent. Most of the scent lock suits that hunters use are charcoal lined from what I've read. Also, I THINK the military used charcoal in their chemical suits...I didn't know charcoal would absorb water if so it's not much a better solution is what I use in my tackle box to keep hooks from rusting and it is to take some old pantie hose cut the foot off and fill it with kitty litter or oil dry and tie a knot in it they are both silica absorbents and store them that will keep it good and dry.