With a 1/2 ton truck, the issue is not the towing capacity - it's the pin weight on the rear axle. Having 4WD decreases your payload, as well, due to the added weight of the front axle and transfer case.
Load the truck up (people, fuel, hitch and junk) and head for the nearest CAT scale. Get separate axle weights. Subtract the scale weight for the rear axle from the GVWRR (rear rating) on the door sticker; that will be what you have left for "payload" or pin weight. Then calculate 20 - 23% of the GVWR (gross weight rating - NOT dry weight) for the fifth wheel. That will be your estimated loaded pin weight. You might be surprised how close you might be with a 1/2 ton truck.
Rob
