According to Fifth Wheel Safe Towing, the F150 3.5L Ecoboost correctly configured is the only half ton capable of towing fifth wheels.
Towing 5th Wheels with half-tonI towed my 10K fiver over 20K miles in 3 years with my 2011 Ecoboost Max Tow and never felt like I needed a bigger truck. At the minimum, get the Max Tow package for an extra 500 lbs of payload. Even better, get the HD Payload package for over 2000 lbs of payload.
Without the HD Payload package, you should add Helwig or Supersprings overloads or the Sumosprings and Bilstein 4600 or 5100 HD shocks.