Ladder

Yeah, a folding ladder would be much easier and many of them are really compact. A telescoping type would probably be the most compact but they often don't have the highest weight ratings so it just depends what you need it to do.

As for mounting it, I agree that you'd need to contact the manufacturer to determine if/where you can mount one. I think there's a reasonable chance that you just can't do it. I'm pretty sure they'd have to plan for a ladder and give you lots of meat in the wall to attach to. After years of RVing one thing I know for sure is there isn't a lot of non-essential material present inside these things. Essential material is often missing for that matter :)

I wouldn’t add a ladder. Buy a collapsible ladder and store inside.

How can you add a ladder, the rear end is taken up by that door isn't it? I'd just get one of these folding ladders and carry it in the garage.

I would call the manufacturer and ask about adding a ladder. Find out if recommended, which one, where to install.

Jerry