A properly equipped F150 will be sufficient for almost any travel trailer in the length you suggest. A fifth wheel will place more weight on the vehicle- ~20-25% versus 10-15% of a travel trailers weight. If you are one to want to adhere to the sticker payload capacity, you'll have a hard time staying under with most fifth wheels unless you opt for a max tow or HD payload optioned truck. For example, a typical F150 SCrew moderately optioned will have a payload in the 1500-1700 pound range. Most fifth wheels in the size range you list- even the ultralites, will have a loaded and ready to camp pin weight of at least 1400-1500 pounds. Some folks think the payload capacities of the F150 is limited mainly by the fact that they don't want them to show higher than the F250 which is limited to a GVWR of 10K, but I don't know any of them personally.