Don't know if you are still in the market for the ladder, if you are, try owlvans.com. I purchased the door mounted spare tire mount and love it. Great design, bomb proof construction and very supportive people. Highly recommend John and the gang.
Interesting idea. I have a 1997 RT 190 Popular with the spare mounted on the rear door. It would be nice, though, to have a ladder there so I could clean the roof mounted solar panel.