Without knowing the weights there is no way to say for certain whether you could or could not tow it.
The problem you have is the relatively short box that comes standard on MegaCab trucks. I believe it is shorter than even a standard 6 foot short bed. If you were to hitch up and if weights were within specs, the first time you tried to back at any angle you could take out the trucks rear window. Slider hitches can help, but are not a cureall on mega cabs.
Couple that with the really soft suspension and high ready to travel weight it is highly unlikely you will not be comfortable putting so much pin weight on the truck.
BTW as a comparison, a TT will place around 12% of its weight on the truck. Whereas a fifth wheel will drop approx 20% of its weight directly on top of the rear axle. To put it more bluntly, with fivers it is not towability, but trucks weight carrying capacity that is key.