Maybe 5% of pickup buyers use
Maybe 5% of pickup buyers use a 5th wheel, but I'll bet way less than 5% of F150's have a 5th wheel. People with that towing need will typically buy at least an F250 due to the limited payload capacity of the F150 versus the high hitch weight of 5th wheels. For example, the "dry" hitch weight of my 5th wheel is 1834 lbs. Hitching that onto an F150 with the heavy duty payload option might work, but you'd be riding the edge of the truck's rated payload, and would have to constantly be thinking about the weight balance of how you're loading the 5th wheel and the number of passengers and other cargo you're putting into the truck.