We have also had a bad ladder experience. we bought a camper after being told they would add a ladder, a feature we really wanted. Then they discovered it could not be added safely due to the blocking not being there from the factory. Oh well, so we got the ladder noted below. Its light weight , 30 lbs i think, supports up to 300 lbs, solid collapsed height about 32 inches i think, and extends to 12.5 feet. I used it a couple weeks ago during a camping trip, it telescopes in and out easily. we used to clean the slides and lube the slide seals and it did good, we didnt use to get up on the roof. We dont want to get up on the roof much.
http://www.extendandclimb.com/
Probably shouldnt be on the roof much anyway. I might have been tempted to hang bikes off it, not such a good idea.
hope you solve your ladder dilemma.