I'm using a 4 step step ladder. It seems the best solution that I have come up with so far. It's stable, strong, folds and is easily storable under the lower couch section when we are not in bunk bed mode.
Mine is similar to this one.
https://smile.amazon.com/Rubbermaid-...i&sr=1-14&th=1
Too many complaints about the ones that are typically given or sold as RV Bunk ladders either hurting peoples feet to walk on (because the ladder rungs are so narrow) or them collapsing or needing to be cut off to maintain a proper angle.