I considered doing the same when I had my 1150 because the roof is so massive. I decided against it for several reasons.
1. As you noted getting up and down is a safety concern even with both hands empty so carrying something up that high didn't appeal to me.
2. The luggage rack was nice to look at but the only open area was where you would climb up on to the roof in front of the ladder, the drivers side had the bathroom power vent and bathroom skylight in the way so it was useless on that side. Unless you wanted to be climbing over the storage putting something on the right was pointless as well so I determined the roof rack was nothing more than a hand hold to climb on to the roof with and more holes to do maintenance on. I'd delete that option if I ever ordered a camper. The only place left really was on either side of the AC and the small space directly behind it but that brought up my other concerns.
3. How would I attach it to the roof. I didn't like the idea of more holes to become potential leaks as there was already enough holes up there for me to contend with.
4. Also was the concern of damaging the roof, not from weight but rather the container constantly in contact rubbing away at the roof membrane. You'd have to put down a barrier or make sure what ever you used to attach it was solid. I guess you could make a bracket and attach it to the roof rack itself but then it would stick up higher than the AC and possibly cause clearance issues.
In the end I found the back seat of the truck or inside the camper was a safer and less hassle place to put my stuff.
I know it's not the answer you were after but just out of curiosity what would you want to put up there if you do this?