Most big box stores have a folding step stool. One step. I keep mine right inside the door of my RV and if I need to, I just grab it, open it, and drop it down on the ground to use as another step. Then I leave it there. This only happens occasionally so not needed every time.
Then if the RV park I'm at has a theft reputation, (I ask at the desk AFTER I've paid) I tie a nylon string to the step and pull it up at night to lock inside. Which would work good in your situation since you're talking about the drivers side door.
Called a '
Folding Step Stool'.
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