We are looking to buy a backpack-style carrier for 5 month old DD, for hillwalking. She's not keen on napping, though: do babies ever sleep in these, or am I going to end up halfway across some desolate moorland with a screaming tired baby extremely close to my ear? She won't sleep in the sling anymore, so I'm worried that a backpack will just be far too exciting - but I'm longing to take advantage of maternity leave and stomp up some hills this summer. Any advice or warnings gratefully received...