I built a large step 30x24x6 inches to help my mom get into the Suburban. Since it is already in the back of the truck I use it as an additional trailer step as needed.
I made the step large so people can step up and stand on it before thinking about taking the next step. It's also nice to just come down the stairs and not really think about placing my foot correctly on a small stool.
I'm not sure how much room you would have to store a step in a class A. But I would build a step as large as I could comfortably transport and handle.
