For best performance, you should be using heavy duty wiring for both the supply and ground return; at least #10 or larger. Some use #4 welding cable for this.
With smaller wiring on a run that long, it will still work, but due to the voltage drop in the wiring, you will only get about 10 amps going to a severely discharged trailer battery, i.e. 10+ hours to get the battery back to about 75% charge.
1999 Winnebago Adventurer 32T Ford V-10