I would stash the pack in a cheap duffle you can lock. Sad to say, but unlocked bags get rifled through fairly regularly, so don't pack any valuables in it-money, camera, GPS, passport (not that you need one for Philmont, just a general suggestion), etc. Someone makes a mesh lockable bag for packs, but never actually seen one except in an ad.

Travel packs with wheels are too heavy for any serious backpacking and the wheels take up too much room, so I would avoid those.