I just bring one pair of glasses, wear them all the time, and put them in a pocket built into my tarptent when I sleep at night. I wear a hat with a brim and have never had a problem with glasses fogging up while I hike, even in the rain -- don't know why. I've worn drill mount (frameless) glasses for over twenty years so I don't have to worry about a lens popping out. Some people shy away from this style of glasses for fear they are fragile but I've never broken anything on any of the pairs I've had in all these years -- I think I am by nature very careful with my stuff. I've spent every night on any trail in a tent and not a shelter so don't have any experience with what to do with my glasses in a shelter.