We use a 16ft extension ladder that we attach to the existing aluminum RV ladder by way of two good quality ratchet straps. We just traveled 4,000 miles with this setup and had zero problems. A check of the tightness of the straps is a mandatory step in the "check at every stop" list and it was never once found to be loose.
To answer the question of why do we carry this beast the answer is simple: I am a person of heft, or phatitude, if you like. I can no longer do the climb straight up a ladder thing and so I need the extension ladder to provide a bit of a slope for me to climb up. Also, I have little faith that the flimsy RV ladder will hold my heft or that it won't pull itself right off of the back of the RV if I happen to lean too much booty out behind my centre of gravity.
Cheers All!
Mike