I have a 25ft (approx.) piece of house wire for a dryer. It has three #10 solid copper and one thin wire for ground. I twisted the ends all together to make one "fat" wire but they are of course in parallel except at the ends. Has very low R between the ends at 25ft.
You could make that a "pair" by just twisting two and two at the ends. The one side with the thin ground wire would be like that part in the modified RV cord.
I even have more long pieces copper water pipe not doing anything left over from a reno. Copper water pipe makes great low R wire! :) (Goes inside a garden hose except at the ends)