Ah - misread which tank capacity. Out of the total weight, not much of a change - that leaves the drag force available even higher.
Going with 30 gallons -> 180 pounds for fuel, ~1900 pounds total; 190 pounds of thrust to keep the plane in the air, leaving 1250 pounds or drag from the banner to absorb the output from the engine.
To get a similar pull from a 20:1 L/D glider tow, the glider could weigh around 25,000 pounds.