As RoyB said. With that adapter, you can run any electric cord from the house to the trailer and then plug in the adapter. The heavier the electric cord, the better it is, but I kept all my trailers plugged in a simple orange 100 foot cord from Wall Mart for years. Of course I did not run the air conditioner, but it did keep the batteries charged and it allowed us to drive-way camp.
Eventually, I got 30 amp RV cords and for years now, have about 150 feet of cord. I keep my current camper plugged in with a 50 foot 30 amp now. I also had installed a 30 amp RV box too, so now we can truly use the camper in it's full function at home.
But, for your purposes, RoyB has it right! Get the adapter and just plug the trailer in.