Went out yesterday to plant a spare key on my new Q2500. Didn't want to do my traditional zip-tie under the bumper 'cause road salt remdered my Mercedes key almost useless.
Discovered the nifty plasitc liner inside the cas fill door, and the little pocket on the front end side. There is also a handy loop formed by the door hinge. I was going to zip tie to the loop, but decided instead to just stick the key to the side with a piece of 2" clear packing tape with a folded-over tab on one end so I would have something to grab. Out of sight, protected, secure. Love it.