My BIL had an 8' bed on his F250, I have a 6.5' on our F150. We've been on a few trips when we both had travel trailers. Both setups worked well. The difference was when we unhitched, and went into town. He did a fair amount of curb hopping to go places I could just fit.
The reason I didn't want a 5.5' bed was that it is too short to fit a golf cart. Here's pics of mine in use:


I had to remove the tailgate so it wouldn't hit the trailer in sharp turns. Consequently, the golf cart couldn't park on the tailgate. It "just fits" on a 6.5' bed.
If you plan on hauling toys, make sure you get the max tow package. Mine included longer leaf springs, a tighter turning radius, HD hitch, integrated brake controller, transmission cooler, etc. This is why my truck doesn't squat when it has a 1000 lb golf cart in the bed. My setup is rated for 1800 lbs payload, 11,100 towing. The TT weighs about 5000 lbs fully loaded. Really a nice setup... but recently moved up to a Class A to haul more toyz!