Aerodynamic and geared for fuel mileage. Gearing will depend on how fast/slow you plan on running. With that weight, 65-68 mph could get you close to 10 mpg with the proper setup. Every gallon of fuel you can save can add up to big money in your pocket! Good luck
First the trailer is critical in this, you have to select it carefully and for the purpose of the freight you are going to haul. Then use any truck (class 7 or 8) with a smaller displacement and multiple gear transmission, geared to the lowest fuel consumption per manufacturer’s specs. A dealer (good one who is experienced in selling trucks not carpet) can give you several options for the driveline and with fuel consumption targets.