I had thought about doing it with our old 210WBS. Even went as far as getting the framing plans for the trailer from CruiserRV. Turns out that the rear framing on the trailer was not laid out in a manner that would take a ladder. A universal ladder could have been added, but, there would not have been any support, aside from the filon, for the attachment. Bad idea in my thinking and I never put one on. If you don't have adequate attachment points, eventually, possibly with the first climb, the holes in the filon will "egg shape" and allow water entry; kiss of death for laminate sided trailers. I carried a collapsible ladder in the TV for the times I needed to get on the roof.
My current trailer has a ladder, installed from the factory and the trailer had the backing plates necessary for installation of the ladder as part of the stock framing. Had I not ordered the ladder option, the backing plates would still have been there and I could have put a ladder on myself as the trailer was designed to have a ladder and they don't bother to make two different frames for those that order the ladder and those that don't. I've found, over the years, that the newer trailers, if they have a "ladder option" from the factory will have the necessary framing and backers whether the ladder is ordered or not, but, trailers that don't have a ladder as an "option" will not and most likely the frame (stud) spacing is not going to be conducive to adding a "universal" ladder.
Had a friend that decided to go ahead and put one on...he figured he'd put his own "backers" in. He used wood plates attached to the inside walls of the trailer with screws long enough to go all the way through to the wood plates; he thought it was a good idea and to him they, the wood plates, didn't look too bad. I thought otherwise about the idea and the way it looked. The holes still eventually "egg shaped" on him because the backer was too far away from the actual stress area. The backer isn't so much to keep the screws from pulling out (they do aid in grip though) as they are to keep the weight from climbing the ladder leveraging the screws down through the filon, egg shaping the holes. Move the backer away from the immediate mounting area and leverage will still allow the screws to deflect up and down and side to side enough to eventually egg shape the holes and break the sealant seal against the filon. His delaminated...took a few years, but, it was a mess when he got rid of the trailer and cost him in resale value.
IMHO, I wouldn't (and I didn't
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