WELCOME TO THE FORUM!
If you have an F150, a ? ton truck, the box does not matter!! IT DOES NOT HAVE THE PAYLOAD TO HAUL ANY FIFTH WHEEL!!
Get your truck weighed with a full tank of gas. Now subtract this from the truck GVWR, shown on a white label on the driver door. This is your real payload. It should be in the neighborhood of 1500#. This is the most weight your truck is designed to carry.
Now add up the weight of all passengers, pets, tools, cargo and firewood carried in the truck. Add 200# for a FW hitch. Subtract this from your payload to find the heaviest FW pin wt you can handle. Since average pin wt is 20% of actual FW weight, multiply by 5 to get the weight of the heaviest LOADED FW you can handle.
EXAMPLE: 400# passengers and pets, 200# tools, cargo and firewood. 200# hitch = 800#.
This leaves only 700# for pin wt, or 3500# GVWR fifth wheel. NO WAY
EXAMPLE: 400# total passengers and cargo in the truck. 200# hitch = 600#
This leaves 900# for pin wt, or a 4500# FW.
A "light weight" 7000# DRY WT FW will weigh 8500# or more after you add propane, water, food, pots and pans, clothing, bed linen and towels. This will have a 1700# pin wt. Now add a FW hitch and passengers........
There IS an alternative - a reasonable size Travel Trailer (TT) (Bumper pull).
While a FW places 20% of its weight on the truck, plus a 200# hitch, a FW places only 10% - 12% of its weight on the tongue, with an 80# WD hitch. In example 1, the 700# pin wt becomes 820# hitch wt, or an 8000# TT Example 2 will have a 1020# hitch wt, or a 10,000# TT. The limiting factor here really becomes the length. The camper is a huge sail, and a 30ft camper will push the truck all over the road on a windy day.
Be very careful NOT to believe the salesman. His priority is selling campers, not your safety. He will say you can yow almost anything on his lot. HE LIES!
Here is how they think: http://www.rvforum.net/SMF_forum/index.php/topic,90933.0.html