Welcome to the forum where a question will give you many answers....some way out there.
I can't help you with a floorplan for 6 people and one you like.
A F250 as any truck doesn't pull trailers determined by the trailers length
However lets look at your F250 which is the same as a F350 SRW other than higher rated rear spring packs in some cases. If your F250 has the camper package or heavy service package it has the same suspension. I weigh all my trucks front and rear axles ...that way I know how much load to carry.
If your truck has 17" tires and wheel at 3195 lbs then the rear suspension has a 6100 rawr which gives around 3000 lbs payload in the bed.
Many F250 came with a optional 18"/20" wheels rated at 3525 Lbs and makes for a 3500 lb payload in the bed.
When looking at 5th wheel trailers pay attention to the trailers dry weight and dry pin weight....the trailer CCC......and its gvwr. There all players in figuring any trailers hitch load.