Probably the first thing you should conceder is the pin weight of the 5er. Get your truck weighed at a Cat scale full of fuel, all gear and passengers that you will be taking on your camping trip and the fifth wheel hitch(around 400 lbs). The Cat Scale will give you the steer axel (front) weight, the drive axel weight (rear) and the total weight of your truck. With that information you will be able to determine the max weight of the camper you plan on towing. The sticker on the driver's side door of your F250 will give you the max payload probably around 3100 lbs or less) and gross rear axel weight rating (probably around 6100 lbs.) When looking at the camper be mindful that the weight on the sticker is an empty weight and does not include any dealer installed options. For your truck I would try for a max fully loaded weight of around 13,000 lbs. With all this in mind you should be able to find a 5er in the 32 to 33 ft (pin to rear bumper) range that will fit your needs.
-BC-
