OK, here's some REAL LIFE experience towing a fifth wheel with our 2012 F-150 EcoBoost, 4WD, Crew Cab.
I special ordered a brand spanking new F-150 EB with the MAX TOW package, PLUS the HD Package. We towed a 2007 Wildcat 32QBBS which has a dry weight of 8900 lbs, but loaded, we weighed right at 10,000 lbs.
It was 35'10" long.
The truck handled it perfectly. We put almost 50,000 miles on the truck towing and for a daily driver (6 miles round trip per day)
When we, actually I, decided to upgrade our fifth wheel, I talked DH into upgrading the truck. We now have an F-250 6.7L.
So, yes, an F-150 will safely tow a fifth wheel, but it will need to have the correct setup to match the fifth wheel.