It's best to check with the manufacturer to see if a ladder can be added to the unit. On some trailers, they don't put the blocking for attaching a ladder unless the trailer has been ordered with a ladder. That was the case when I wanted to add a ladder to my old Sunline trailer. But, when I wanted to add one to our 2014 Winnebago 2201 DS, it wasn't a problem, and it was cheaper to go to the factory and have them install it rather than trying to order one and do it myself as shipping costs on a ladder isn't cheap.
Retired but busier than ever!
2013 Winnebago 2201DS - 6,200 lbs. or so loaded!
2007 Tundra 5.7