I bookmarked this because it said it would withstand Florida humidity. It uses bread flour and it uses extra butter.
http://jacksonville.com/tu-online/stories/121897/1218Ging.html More butter seems wrong to me. The crackers they served to soldiers in old days were nothing more than flour, water and salt and they lasted forever. Also, salt dough ornaments are made with just flour, salt and water. You would think that adding more butter wouldn't be good. On the other hand, more butter in a cookie makes it crisper. Maybe crisper = humidity proof. I don't know. I've never tried it.