A step ladder is designed to hang on an OEM ladder on a recreational vehicle (“RV”) while traveling on the road. The step ladder comprises a hanger bracket to hang the step ladder on the OEM ladder. The bracket is wider than a width of the legs of the step ladder to project over a rung of the OEM ladder. A hook on the bracket grabs the rung of the OEM ladder. The step ladder may be further secured to the OEM ladder by inserting a lock through the bracket and through or adjacent to the rung of the OEM ladder, or by inserting a lock through another rung of the OEM ladder and a retaining tab of the step ladder. A stabilizer attached to the step ladder and the RV can further stabilize the ladder when desired.