I have a large travel pack that I check in all the time, and it's never had any damage (though it really doesn't have anything loose to damage). I've seen some backpacks wrapped in plastic bags, but not sure if that is provided by the airline or the traveler (if the airline, mine never gets put in a bag). I've also seen backpacks inserted in some type of travel bags, but to me that just seems like something more to bring along that you'd have no use for.