Take stuff out of the trailer and put it in the RV. If you travel that far with an overloaded trailer you will have great stories and great expenses. Don't forget to cross your chains under the tongue. If the chains are too long just twist them before your hook them on. The tongue weight should be 10 to 15% of the trailer weight. Get a long 2X10 and pivot point(big rock or block), figure your weight and use some math to figure out where you on one end of the 2X10 the other end under the coupler will balance out. The other way to do it start out on a deserted road and slowly increase your speed. If the trailer starts fish tailing, you don't have enough weight on the tongue. Make sure the trailer brakes work.
Mike