Justin. That must be one huge fifth wheel camper. I'd go with the F350 Crew Cab dually, basically getting the same engine/trans unless you go for a F650 then you can get a different engine package.
Yea, go with a F350. It could handle the weight. What are you going to tow that is 15k lbs? You won't need a F450 and that would be over kill. Stick with the dually also.
Wow that is bad ass and big! Is that what you have or just a pic of it? Is that your existing truck hooked up to it?
Like Cowboy said, you might want to get the F450 now that I see the thing. I think the F350 will still be ok, but better to be safe then sorry if you can afford the F450. What size truck is pulling it in that pic, a F250?