We have the truck in my signature. Pulling our 32' fifth wheel which weighs around 14,500# loaded, we average 12.090 MPG (this is the average both pulling & solo). With our slide-in truck camper (not a pop-up, though...it's a 9.5' Eagle Cap which weighs, loaded, over 4,000#), we average 13.750 MPG (almost 100% with the camper on rather than solo).
I would think that with a lighter, lower profile camper would give you even better fuel mileage.