One of the reasons for the code specifications in household electrical
wiring is the rodent protection that is introduced in the sheath that covers the wires.
Extension cords are under a different set of standards and MAY NOT have the chemicals in their coverings as household wiring does.
If you have concerns of rodents entering your camper then it would be prudent to wire in accordance with the electrical
code for campers. (The code may not be the same as for a household)
electric cable assembly and method for protecting an electric cable assembly for rendering the cable repellent to rodent attacks. A non-lethal toxic chemical, such as lithium chloride, which produces lithium ions when dissolved in the saliva of an animal, is incorporated in an electric cable as either a layer within the electric cable assembly around the circumference and along the length of the cable assembly or by providing a coating on the surface of the electric cable assembly by spraying or painting
thereon a mixture containing, for example, lithium chloride. A protective layer or coating may be provided around the layer or coating of the lithium ion producing chemical to protect it against moisture or other environmental conditions.