Hi,
Download the Ford towing guide for 2015 here.
http://www.fleet.ford.com/towing-guides/THen look on page #10 and you will see that the SRW F-350 has a cargo rating and GVWR. Subtract the cargo rating from the GVWR and you will get a close 'curb weight'.
So the regular cab 8' bed F-350 DRW cargo rating and GVWR is 13,500 and 6839 so curb weight of the regular cab dually is about 6,660 pounds.
Crew cab SRW SWB is 10,200 pound GVWR - the cargo rating of 2,973 = curb weight about 7,200 pounds.
Crew cab SRW LWB is 10,500 pound GVWR - 3,139 = curb weight about 7,300 pounds.
Then look up the GCVWR on page #18.
The 6.2L gas with 4.30:1 rear axle ratio is 22,200 for the SRW and 22,800 for the dually gas engine.
If you will have 600 pounds of stuff in the pickup, and then add 2,000 pounds of pin weight, then the truck will have a curb weight of say 7,300 + 200 pound hitch or 7,500 pounds. Then add the 600# and 2,000 pin weight, you will be at 8,100 for the truck and 10,100 for the truck and trailer pin weight.
Take the 22,200 - the 8,100 truck weight (don't deduct the pin weight twice) and you have 14,100 pounds for the total weight of the trailer, and about 2,200 pounds available pin weight capacity before exceeding the GVWR of the truck.
You do not have as much trailer capacity as the chart shows on page #18. However going over the GCVWR by a few pounds is acceptable. Make sure that you are well within the GVWR of the truck, and under the axle weight ratings.
Good luck!
Fred.