Dual Rear or Single Rear Wheels on Tow Truck?

Don't get a 3/4 ton - The F250 is virtually the same truck as the F350 SRW (almost identical price as well) with the payload of a F150. I would not want a dually for my RV which weighs about 15,000 lbs. I pull a gooseneck with my F350 short box that weighs up to 30,000 and realize that a dually would be better suited for that trailer but the SRW shortbox handles it very well and suits me better than a dually would when unloaded, so it's a compromise. With Ford you have to go to a 3.73 axle ratio and smaller tires once you spec duals which reduces the fuel economy of the truck. If you buy a SRW you will likely save more than enough on fuel and tires to cover the cost of prematurely replacing the truck with a dually if you end up getting a 17 - 20,000 lb rv 5 years down the road.