According to the dodge web-site the pay-load/ pin weight limit is 1985 lbs and trailer GVW is 12,800 lbs. to me that limits you to some of the lighter Sundances for a fifth wheel.
On the same note, I know a LOT of people here will tell you that you can tow more, but I like to obey what engineers say is safe to do, because I am one too. I bought a F-450 for a reason. If there is not a difference in a 3/4 and a 1 ton other than springs, then why do they not just sell everyone a 3/4 with air-bags to level out the over-loaded truck? Towing more than what a truck is rated is not just dangerous to you and your family. it is dangerous to everyone else on the road. I will probably catch some flack for saying that it is dangerous and irresponsible, but this is just how I feel.